Fix strict flags compilation error in box pack

No need to check q >= 0 in quad_flag() since q is
an unsigned int argument.

source/blender/blenlib/intern/boxpack2d.c

@@ -87,7 +87,7 @@ typedef struct BoxVert {
 
 BLI_INLINE int quad_flag(unsigned int q)
 {
-	BLI_assert(q < 4 && q >= 0);
+	BLI_assert(q < 4);
 	return (1 << q);
 }