Fix -wformat-overflow in ABC_Init

Fixes the following warnings

```
load_abc.cpp:2374:42: warning: ‘%ld’ directive writing between 1 and 20 bytes into a region of size 18 [-Wformat-overflow=]
 2374 |                         sprintf(buf,"%s=-%ld",ABC_ENV_NORANDOMPICK,retval->pickrandom+2);
      |                                          ^~~
load_abc.cpp:2374:37: note: directive argument in the range [-9223372036854775806, 9223372036854775807]
 2374 |                         sprintf(buf,"%s=-%ld",ABC_ENV_NORANDOMPICK,retval->pickrandom+2);
      |                                     ^~~~~~~~~
load_abc.cpp:2374:32: note: ‘sprintf’ output between 24 and 43 bytes into a destination of size 40
 2374 |                         sprintf(buf,"%s=-%ld",ABC_ENV_NORANDOMPICK,retval->pickrandom+2);
      |                         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Author: glebm

src/load_abc.cpp

@@ -2361,7 +2361,7 @@ BOOL CSoundFile::TestABC(const BYTE *lpStream, DWORD dwMemLength)
 // =====================================================================================
 static ABCHANDLE *ABC_Init(void)
 {
-	static char buf[40];
+	static char buf[43];
 	ABCHANDLE   *retval;
 	char *p;
 	retval = (ABCHANDLE *)calloc(1,sizeof(ABCHANDLE));