Fix segfault in testrunner

src/common/LuaSupport.cpp

@@ -164,23 +164,21 @@ bool Surge::LuaSupport::setSurgeFunctionEnvironment(lua_State *L)
     // stack is now f>t>(m). Pop m
     lua_pop(L, 1);
 
-    // clear global table
-    int stacktest = lua_gettop(L);
+    // retrieve the "global" table
     lua_getglobal(L, "global");
-    int stacktest2 = lua_gettop(L);
-    if (lua_type(L, -1) == LUA_TTABLE && lua_type(L, -2) == LUA_TTABLE &&
-        (stacktest2 - stacktest == 1))
-    {
+    // check if the retrieved value is a table
+    if (lua_istable(L, -1)) {
         lua_pushnil(L);
-        while (lua_next(L, -2))
-        {
+        // set table entries to nil
+        while (lua_next(L, -2)) {
             lua_pop(L, 1);        // pop value
             lua_pushvalue(L, -1); // duplicate the key
             lua_pushnil(L);
             lua_settable(L, -4); // clear the key
         }
-        lua_pop(L, 1);
     }
+    // pop the retrieved value (either table or nil) from the stack
+    lua_pop(L, 1);
 
     // and now we are back to f>t so we can setfenv it
     lua_setfenv(L, -2);