Various fixes to vm_interpreted.c:

- Add opStack protection
- Fix dataMask check for OP_BLOCK_COPY
- Add instruction number check for conditional jumps
- Make errors in VM_PrepareInterpreter nonfatal

code/qcommon/vm.c

@@ -949,3 +949,25 @@ void VM_LogSyscalls( int *args ) {
 	fprintf(f, "%i: %p (%i) = %i %i %i %i\n", callnum, (void*)(args - (int *)currentVM->dataBase),
 		args[0], args[1], args[2], args[3], args[4] );
 }
+
+/*
+=================
+VM_BlockCopy
+Executes a block copy operation within currentVM data space
+=================
+*/
+
+void VM_BlockCopy(unsigned int dest, unsigned int src, size_t n)
+{
+	unsigned int dataMask = currentVM->dataMask;
+
+	if ((dest & dataMask) != dest
+	|| (src & dataMask) != src
+	|| ((dest + n) & dataMask) != dest + n
+	|| ((src + n) & dataMask) != src + n)
+	{
+		Com_Error(ERR_DROP, "OP_BLOCK_COPY out of range!");
+	}
+
+	Com_Memcpy(currentVM->dataBase + dest, currentVM->dataBase + src, n);
+}