game.c: fix out-of-bounds write in G_GetSubString().

git-svn-id: https://svn.eduke32.com/eduke32@3852 1a8010ca-5511-0410-912e-c29ae57300e0

polymer/eduke32/source/game.c

@@ -379,7 +379,7 @@ char* G_GetSubString(const char *text, const char *end, const int32_t iter, cons
         ++counter;
     }
 
-    line[++counter] = '\0';
+    line[counter] = '\0';
 
     return line;
 }