graphics/grX11su1.c: Dereference of null pointer

Looks like the code below requires w!=NULL to do anything useful.
So when w==NULL we don't continue processing X11 Event.

SonarCloud
graphics/grX11su1.c:842 Dereference of null pointer
https://sonarcloud.io/project/issues?open=AZJB163RNGfDNup0Ri4o&id=dlmiles_magic

graphics/grX11su1.c

@@ -835,6 +835,8 @@ grX11Stdin()
 		    entry = HashLookOnly(&grX11WindowTable,grCurrent.window);
 	            w = (entry)?(MagWindow *)HashGetValue(entry):0;
 	            grCurrent.mw=w;
+	            if(!w)
+	                break;
 
 		    screenRect.r_xbot = ExposeEvent->x;
             	    screenRect.r_xtop = ExposeEvent->x+ExposeEvent->width;