add global variable name check with other globals

Author: Elektryk-Andrzej

Code/ScriptSystem/Script.cs

@@ -368,8 +368,8 @@ public static void CheckForVariableNameCollisions(Variable newVariable, IEnumera
             .Any(gv => Variable.AreSyntacticallySame(gv, newVariable)))
         {
             throw new CustomScriptRuntimeError(
-                $"Tried to create a local variable '{newVariable}', " +
-                $"but there is already a global variable with the same name."
+                $"Tried to create a variable '{newVariable}', " +
+                $"but there already exists a variable with the same name."
             );
         }
     }

Code/VariableSystem/VariableIndex.cs

@@ -77,6 +77,7 @@ public static void Initialize()
 
     public static void AddGlobalVariable(Variable variable)
     {
+        Script.CheckForVariableNameCollisions(variable, GlobalVariables);
         foreach (var runningScript in Script.RunningScripts)
         {
             Script.CheckForVariableNameCollisions(variable, runningScript.LocalVariables);