null check dynamic casts (#4548)

# Description

Resolves stellar/stellar-core-internal#307

Checks for null after dynamic casting pointers.

# Checklist
- [x] Reviewed the
[contributing](https://github.com/stellar/stellar-core/blob/master/CONTRIBUTING.md#submitting-changes)
document
- [x] Rebased on top of master (no merge commits)
- [x] Ran `clang-format` v8.0.0 (via `make format` or the Visual Studio
extension)
- [x] Compiles
- [x] Ran all tests
- [ ] If change impacts performance, include supporting evidence per the
[performance
document](https://github.com/stellar/stellar-core/blob/master/performance-eval/performance-eval.md)

src/ledger/LedgerTxnAccountSQL.cpp

@@ -628,6 +628,7 @@ class BulkLoadAccountsOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnClaimableBalanceSQL.cpp

@@ -109,6 +109,7 @@ class BulkLoadClaimableBalanceOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnConfigSettingSQL.cpp

@@ -112,6 +112,7 @@ class bulkLoadConfigSettingsOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnContractCodeSQL.cpp

@@ -117,6 +117,7 @@ class BulkLoadContractCodeOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnContractDataSQL.cpp

@@ -150,6 +150,7 @@ class BulkLoadContractDataOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnDataSQL.cpp

@@ -452,6 +452,7 @@ class BulkLoadDataOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnLiquidityPoolSQL.cpp

@@ -129,6 +129,7 @@ class BulkLoadLiquidityPoolOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnOfferSQL.cpp

@@ -798,6 +798,7 @@ class BulkLoadOffersOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnTTLSQL.cpp

@@ -116,6 +116,7 @@ class BulkLoadTTLOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);

src/ledger/LedgerTxnTrustLineSQL.cpp

@@ -465,6 +465,7 @@ class BulkLoadTrustLinesOperation
         }
         auto sqliteStatement =
             dynamic_cast<soci::sqlite3_statement_backend*>(be);
+        releaseAssertOrThrow(sqliteStatement);
         auto st = sqliteStatement->stmt_;
 
         sqlite3_reset(st);