Fix/workaround T51007: Material viewport mode crash on node with more than 64 outputs

Ideally we need to find a way to remove such a static limit here, but it's not so
trivial to implement for texture nodes. Requires some bigger system redesign there.

Just raising limit for now, which is fine for modern systems.

source/blender/blenkernel/BKE_node.h

@@ -49,7 +49,7 @@
 #include "RNA_types.h"
 
 /* not very important, but the stack solver likes to know a maximum */
-#define MAX_SOCKET	64
+#define MAX_SOCKET	512
 
 struct bContext;
 struct bNode;