Prevent accidental double-frees

- matcher.cpp, survey.cpp: setting the state pointer to null/nullptr in ::shutdown() to prevent errors caused by accidental double-frees - an additional check if the pointer is null already is not necessary as the standard guarantees that nothing happens if delete is called on a nullpointer

Co-Authored-By: Alan <3719547+lethosor@users.noreply.github.com>

plugins/embark-assistant/matcher.cpp

@@ -68,7 +68,7 @@ namespace embark_assist {
             embark_assist::defs::mid_level_tiles mlt;
         };
 
-        static states *state;
+        static states *state = nullptr;
 
         //=======================================================================================
 
@@ -2731,6 +2731,7 @@ void embark_assist::matcher::setup() {
 
 void embark_assist::matcher::shutdown() {
     delete state;
+    state = nullptr;
 }
 
 //=======================================================================================

plugins/embark-assistant/survey.cpp

@@ -75,7 +75,7 @@ namespace embark_assist {
             uint16_t max_inorganic;
         };
 
-        static states *state;
+        static states *state = nullptr;
 
         //=======================================================================================
 
@@ -2548,5 +2548,6 @@ void embark_assist::survey::survey_embark(embark_assist::defs::mid_level_tiles *
 
 void embark_assist::survey::shutdown() {
     delete state;
+    state = nullptr;
 }