- fixed GCC warnings and errors

(Is there anyway to tone down GCC's warning level? It outputs too many false positives for potentially uninitialized variables in which the genuine errors get drowned.)

src/swrenderer/things/r_decal.cpp

@@ -166,6 +166,10 @@ namespace swrenderer
 		// Get the top and bottom clipping arrays
 		switch (decal->RenderFlags & RF_CLIPMASK)
 		{
+		default:
+			// keep GCC quiet.
+			return;
+
 		case RF_CLIPFULL:
 			if (curline->backsector == NULL)
 			{