gh-87092: avoid gcc warning on uninitialized struct field in assemble…

[corona10]

….c (part2)

 Python/assemble.c: In function ‘_PyAssemble_MakeCodeObject’: Python/assemble.c:130:9: warning: ‘handler.h_startdepth’ may be used uninitialized in this function [-Wmaybe-uninitialized] int depth = handler->h_startdepth - 1; ^~~~~ Python/assemble.c:147:34: note: ‘handler.h_startdepth’ was declared here _PyCompile_ExceptHandlerInfo handler; ^~~~~~~ 

• Issue: Split compiler into code-gen, optimizer and assembler. #87092

[corona10]

@iritkatriel It will be the last one.