wcolorpanel.c: Remove warning in rgbIntToChar

This patch removes this warning. The default case should not be used.

wcolorpanel.c: In function ‘rgbIntToChar’:
wcolorpanel.c:2392:2: warning: ‘format’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  sprintf(tmp, format, value[1]);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Rodolfo García Peñas (kix) <kix@kix.es>

WINGs/wcolorpanel.c

@@ -2385,6 +2385,8 @@ void rgbIntToChar(W_ColorPanel *panel, int *value)
 	case RGBhex:
 		format = "%0X";
 		break;
+	default:
+		format = "";
 	}
 
 	sprintf(tmp, format, value[0]);