Fix public return value being always overwritten in exec_helper()
Fix public return value being always overwritten in exec_helper()

Store AMX pointer in ecx instead of eax in emit_exec_helper() as eax
holds the function's return value after the call.

This fixes issue #34.

Zeex/samp-plugin-jit,oscar-broman/samp-plugin-jit,Zeex/samp-plugin-jit,oscar-broman/samp-plugin-jit