Fix 32 bit mode reading long in readInt syscall

[DvvCz]

Fixes #93

Let me know if you'd rather have the readLong/readInt deduplicated, or fixed in another way.

Tested with the given reproduction case in the issue:

li a7, 5
ecall
li a7, 1
ecall
mv a0, a0
ecall

Throws error on 32 bit, prints identical number twice on 64 as expected.

[privat]

Thank you!

[github-actions]

Test Results

12 files  ±0  12 suites  ±0   36s ⏱️ ±0s
 8 tests ±0   8 ✅ ±0  0 💤 ±0  0 ❌ ±0 
24 runs  ±0  24 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 4716fa4. ± Comparison against base commit b0cb517.