Bug#984422: xwelltris: ftbfs with GCC-11

[Nilesh Patra]

control: tags -1 patch

The  patch fixes this if seems ok, please consider to apply

Nilesh

--- a/src/sdl/sdlwelldrawing.cxx
+++ b/src/sdl/sdlwelldrawing.cxx
@@ -72,7 +72,7 @@
 
     fields[i]=SDL_DisplayFormat(surface);
     SDL_FreeSurface(surface);
-    if(fields[i]>0)
+    if(fields[i]!=0)
         clear_field(i);
     }
     bg_color=colors[BackColor];