[prism/compiler] end_cursor should never be NULL

This fixes a failed assertion reported to SimpleCov

simplecov-ruby/simplecov#1113

This can be repro'd as follows:

1. Create a file `test.rb` containing the following code

```
@foo&.(@bar)
```

2. require it with branch coverage enabled

```
ruby -rcoverage -e "Coverage.start(branches: true); require_relative 'test.rb'"
```

The assertion is failing because the Prism compiler is incorrectly
detecting the start and end cursor position of the call site for the
implicit call .()

This patch replicates the parse.y behaviour of setting the default
end_cursor to be the final closing location of the call node.

This behaviour can be verified against `parse.y` by modifying the test
command as follows:

```
ruby --parser=parse.y -rcoverage -e "Coverage.start(branches: true); require_relative 'test.rb'"
```

[Bug #20866]

prism_compile.c

@@ -3630,6 +3630,7 @@ pm_compile_call(rb_iseq_t *iseq, const pm_call_node_t *call_node, LINK_ANCHOR *c
             const uint8_t *end_cursor = cursors[0];
             end_cursor = (end_cursor == NULL || cursors[1] == NULL) ? cursors[1] : (end_cursor > cursors[1] ? end_cursor : cursors[1]);
             end_cursor = (end_cursor == NULL || cursors[2] == NULL) ? cursors[2] : (end_cursor > cursors[2] ? end_cursor : cursors[2]);
+            if (!end_cursor) end_cursor = call_node->closing_loc.end;
 
             const pm_line_column_t start_location = PM_NODE_START_LINE_COLUMN(scope_node->parser, call_node);
             const pm_line_column_t end_location = pm_newline_list_line_column(&scope_node->parser->newline_list, end_cursor, scope_node->parser->start_line);

test/coverage/test_coverage.rb

@@ -463,6 +463,8 @@ def test_branch_coverage_for_safe_method_invocation
         [:"&.", 3, 7, 0, 7,  6] => {[:then,  4, 7, 0, 7,  6]=>0, [:else,  5, 7, 0, 7,  6]=>1},
         [:"&.", 6, 8, 0, 8, 10] => {[:then,  7, 8, 0, 8, 10]=>1, [:else,  8, 8, 0, 8, 10]=>0},
         [:"&.", 9, 9, 0, 9, 10] => {[:then, 10, 9, 0, 9, 10]=>0, [:else, 11, 9, 0, 9, 10]=>1},
+        [:"&.", 12, 10, 0, 10, 6] => {[:then, 13, 10, 0, 10, 6] => 0, [:else, 14, 10, 0, 10, 6] => 1},
+        [:"&.", 15, 11, 0, 11, 5] => {[:then, 16, 11, 0, 11, 5] => 0, [:else, 17, 11, 0, 11, 5] => 1},
       }
     }
     assert_coverage(<<~"end;", { branches: true }, result)
@@ -475,6 +477,8 @@ class Dummy; def foo; end; def foo=(x); end; end
       b&.foo
       c&.foo = 1
       d&.foo = 1
+      d&.(b)
+      d&.()
     end;
   end