Avoid an assertion failure if haloes are disabled.

Moved the assertion after the test whether haloes are enabled, fixes
bug #14297.

changelog

@@ -42,6 +42,7 @@ Version 1.7.5+svn:
      when victory_when_enemies_defeated="yes")
    * Various cleanups to the gui2 code
    * Remove position info from unit list
+   * Avoid an assertion failure if haloes are disabled (bug #14297)
 
 Version 1.7.5:
  * Campaigns:

src/halo.cpp

@@ -324,10 +324,10 @@ void remove(int handle)
 
 void unrender(std::set<map_location> invalidated_locations)
 {
-	assert(invalidated_haloes.size() == 0);
 	if(preferences::show_haloes() == false || haloes.size() == 0) {
 		return;
 	}
+	assert(invalidated_haloes.size() == 0);
 
 	// Remove expired haloes
 	std::map<int, effect>::iterator itor = haloes.begin();