Add NULL_VECTOR

plugins/include/amxconst.inc

@@ -49,6 +49,11 @@ public stock const MaxClients;
  */
 public stock const NULL_STRING[1];
 
+/**
+ * Pass this into certain functions to act as a C++ NULL
+ */
+public stock const Float:NULL_VECTOR[3];
+
 /**
  * The maximum buffer size required to store a clients name.
  */