better callstack for null calls

[mmozeiko]

This improves callstack in win32 unhandled exception handler when indirect call to NULL happens. Before no call stack was printed at all, so it was hard to know what happened. Now call stack explicitly will print out [NULL] stack entry + rest of call stack entries. This is done by manually looking up return address from call stack when possible.

Also fixes wine compatibility for os_commit function. Wine does not support RIO buffer functions.

Before:

--- Fatal Exception ---
A fatal exception (code 0xc0000005) occurred. The process is terminating.

Version: 0.9.25 [5b6ffd5a-dirty]

After:

--- Fatal Exception ---
A fatal exception (code 0xc0000005) occurred. The process is terminating.

Create a new issue with this report at https://github.com/EpicGamesExt/raddebugger/issues.

Call stack:
1. [NULL]
2. [0x1400defb7] os_commit +87, os_core_win32.c line 214
3. [0x1400d5d2d] arena_alloc_ +397, base_arena.c line 38
4. [0x14013ac32] w32_entry_point_caller +882, os_core_win32.c line 1786
5. [0x14013b64b] wmain +27, os_core_win32.c line 1888
6. [0x140248fc0] __scrt_common_main_seh +268, exe_common.inl line 288
7. [0x6fffffa31469] kernel32
8. [0x6fffffc10d2b] ntdll

Version: 0.9.25 [98c90720-dirty]