Fix use-after-free error in wIconStore reported by Coverity

The function always returns the filename where the icon have been saved,
but in the case where the save operation failed we would free the memory
for that file name, yet still return this pointer like if it were valid.

Took opportunity to remove redundant free(path) which is done a couple
lines later, because redundancy is a source of problem for code
maintenance.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

src/icon.c

@@ -518,9 +518,8 @@ char *wIconStore(WIcon *icon)
 	}
 
 	if (!RSaveImage(image, path, "XPM")) {
-		wfree(path);
 		wfree(filename);
-		path = NULL;
+		filename = NULL;
 	}
 
 	wfree(path);