Merge branch 'fix-playintro-crash' into 'next'

Fix intro crash

See merge request STJr/SRB2!1310

src/w_wad.c

@@ -1747,6 +1747,9 @@ void *W_CachePatchNum(lumpnum_t lumpnum, INT32 tag)
 
 void W_UnlockCachedPatch(void *patch)
 {
+	if (!patch)
+		return;
+
 	// The hardware code does its own memory management, as its patches
 	// have different lifetimes from software's.
 #ifdef HWRENDER