Allow scripted faction leaving using PCLowerRank (feature #5036)

CHANGELOG.md

@@ -115,6 +115,7 @@
     Feature #5010: Native graphics herbalism support
     Feature #5031: Make GetWeaponType function return different values for tools
     Feature #5033: Magic armor mitigation for creatures
+    Feature #5036: Allow scripted faction leaving
     Task #4686: Upgrade media decoder to a more current FFmpeg API
     Task #4695: Optimize Distant Terrain memory consumption
     Task #4721: Add NMake support to the Windows prebuild script

apps/openmw/mwmechanics/npcstats.cpp

@@ -85,7 +85,9 @@ void MWMechanics::NpcStats::lowerRank(const std::string &faction)
     std::map<std::string, int>::iterator it = mFactionRank.find(lower);
     if (it != mFactionRank.end())
     {
-        it->second = std::max(0, it->second-1);
+        it->second = it->second-1;
+        if (it->second < 0)
+            mFactionRank.erase(it);
     }
 }