krnl386.exe: Fix a potential leak and NULL dereference in DPMI_xrealloc.

dlls/krnl386.exe16/int31.c

@@ -266,11 +266,11 @@ static void DPMI_xfree( LPVOID ptr )
 static LPVOID DPMI_xrealloc( LPVOID ptr, DWORD newsize )
 {
     MEMORY_BASIC_INFORMATION        mbi;
-    LPVOID                          newptr;
 
-    newptr = DPMI_xalloc( newsize );
     if (ptr)
     {
+        LPVOID newptr;
+
         if (!VirtualQuery(ptr,&mbi,sizeof(mbi)))
         {
             FIXME( "realloc of DPMI_xallocd region %p?\n", ptr );
@@ -289,11 +289,17 @@ static LPVOID DPMI_xrealloc( LPVOID ptr, DWORD newsize )
         if (newsize <= mbi.RegionSize)
             return ptr;
 
+        newptr = DPMI_xalloc( newsize );
+        if (!newptr)
+            return NULL;
+
         memcpy( newptr, ptr, mbi.RegionSize );
         DPMI_xfree( ptr );
-    }
 
         return newptr;
+    }
+
+    return DPMI_xalloc( newsize );
 }