os2/SDL_sysfilesystem.c: fix crash if one of the parameters is NULL

Has been happening with testfilesystem from 2.0.6 and newer because
of commit 572a721879ef.

Also set error strings in certain error conditions.

Also applied coding style / whitespace fixes, while I was there.

src/filesystem/os2/SDL_sysfilesystem.c

@@ -40,80 +40,88 @@ SDL_GetBasePath(void)
 {
   PTIB       tib;
   PPIB       pib;
-  ULONG      ulRC = DosGetInfoBlocks( &tib, &pib );
+  ULONG      ulRC = DosGetInfoBlocks(&tib, &pib);
   PCHAR      pcEnd;
   ULONG      cbResult;
   CHAR       acBuf[_MAX_PATH];
-  
-  if ( ulRC != NO_ERROR )
-  {
-    debug( "DosGetInfoBlocks() failed, rc = %u", ulRC );
+
+  if (ulRC != NO_ERROR) {
+    debug("DosGetInfoBlocks() failed, rc = %u", ulRC);
     return NULL;
   }
 
-  pcEnd = SDL_strrchr( pib->pib_pchcmd, '\\' );
-  if ( pcEnd != NULL )
+  pcEnd = SDL_strrchr(pib->pib_pchcmd, '\\');
+  if (pcEnd != NULL)
     pcEnd++;
-  else
-  {
-    if ( pib->pib_pchcmd[1] == ':' )
+  else {
+    if (pib->pib_pchcmd[1] == ':')
       pcEnd = &pib->pib_pchcmd[2];
-    else
+    else {
+      SDL_SetError("No path in pib->pib_pchcmd");
       return NULL;
+    }
   }
 
   cbResult = pcEnd - pib->pib_pchcmd;
-  SDL_memcpy( acBuf, pib->pib_pchcmd, cbResult );
+  SDL_memcpy(acBuf, pib->pib_pchcmd, cbResult);
   acBuf[cbResult] = '\0';
 
-  return OS2_SysToUTF8( acBuf );
+  return OS2_SysToUTF8(acBuf);
 }
 
 char *
 SDL_GetPrefPath(const char *org, const char *app)
 {
-  PSZ        pszPath = SDL_getenv( "HOME" );
+  PSZ        pszPath;
   CHAR       acBuf[_MAX_PATH];
   int        lPosApp, lPosOrg;
-  PSZ        pszApp, pszOrg = OS2_UTF8ToSys( org );
+  PSZ        pszApp, pszOrg;
 
-  if ( pszOrg == NULL )
-  {
-    SDL_OutOfMemory();
-    return NULL;
+  if (!app) {
+      SDL_InvalidParamError("app");
+      return NULL;
   }
 
-  if ( pszPath == NULL )
-  {
+  pszPath = SDL_getenv( "HOME" );
+  if (!pszPath) {
     pszPath = SDL_getenv( "ETC" );
-    if ( pszPath == NULL )
+    if (!pszPath) {
+      SDL_SetError("HOME or ETC environment not set");
       return NULL;
+    }
   }
 
-  lPosApp = SDL_snprintf( acBuf, sizeof(acBuf) - 1, "%s\\%s", pszPath, pszOrg );
-  SDL_free( pszOrg );
-  if ( lPosApp < 0 )
+  if (!org) {
+    lPosApp = SDL_snprintf(acBuf, sizeof(acBuf) - 1, "%s", pszPath);
+  } else {
+    pszOrg = OS2_UTF8ToSys(org);
+    if (!pszOrg) {
+      SDL_OutOfMemory();
+      return NULL;
+    }
+    lPosApp = SDL_snprintf(acBuf, sizeof(acBuf) - 1, "%s\\%s", pszPath, pszOrg);
+    SDL_free(pszOrg);
+  }
+  if (lPosApp < 0)
     return NULL;
 
-  DosCreateDir( acBuf, NULL );
+  DosCreateDir(acBuf, NULL);
 
-  pszApp = OS2_UTF8ToSys( app );
-  if ( pszApp == NULL )
-  {
+  pszApp = OS2_UTF8ToSys(app);
+  if (!pszApp) {
     SDL_OutOfMemory();
     return NULL;
   }
 
-  lPosOrg = SDL_snprintf( &acBuf[lPosApp], sizeof(acBuf) - lPosApp - 1, "\\%s",
-                          pszApp );
-  SDL_free( pszApp );
-  if ( lPosOrg < 0 )
+  lPosOrg = SDL_snprintf(&acBuf[lPosApp], sizeof(acBuf) - lPosApp - 1, "\\%s", pszApp);
+  SDL_free(pszApp);
+  if (lPosOrg < 0)
     return NULL;
 
-  DosCreateDir( acBuf, NULL );
+  DosCreateDir(acBuf, NULL);
   *((PUSHORT)&acBuf[lPosApp + lPosOrg]) = (USHORT)'\0\\';
 
-  return OS2_SysToUTF8( acBuf );
+  return OS2_SysToUTF8(acBuf);
 }
 
 #endif /* SDL_FILESYSTEM_OS2 */