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:895 Dereference of null pointer
https://sonarcloud.io/project/issues?open=AZJB163RNGfDNup0Ri4p&id=dlmiles_magic

graphics/grX11su1.c

@@ -890,6 +890,8 @@ grX11Stdin()
 
 		entry = HashLookOnly(&grX11WindowTable, VisEvent->window);
 		w = (entry)?(MagWindow *)HashGetValue(entry):0;
+		if(!w)
+		    break;
 
 		switch(VisEvent->state)
 		{