Fixed compiler warning.

Based on fread specification, it returns number of elements which has been read.
Here is declared one element with size of whole file (len), so returned value should be always equal to 1.

src/scriptengine/script_engine.cpp

@@ -107,7 +107,7 @@ namespace Scripting
         script.resize(len);
         int c = fread(&script[0], len, 1, f);
         fclose(f);
-        if (c == NULL)
+        if (c != 1)
         {
             Log::error("Scripting", "Failed to load script file.");
             return "";