Correct Dispel effect (use magnitude as chance)

apps/openmw/mwmechanics/activespells.cpp

@@ -169,9 +169,16 @@ namespace MWMechanics
         }
     }
 
-    void ActiveSpells::purgeAll()
+    void ActiveSpells::purgeAll(float chance)
     {
-        mSpells.clear();
+        for (TContainer::iterator it = mSpells.begin(); it != mSpells.end(); )
+        {
+            int roll = std::rand()/ (static_cast<double> (RAND_MAX) + 1) * 100; // [0, 99]
+            if (roll < chance)
+                mSpells.erase(it++);
+            else
+                ++it;
+        }
         mSpellsChanged = true;
     }
 

apps/openmw/mwmechanics/activespells.hpp

@@ -82,8 +82,8 @@ namespace MWMechanics
             /// Remove all active effects with this id
             void purgeEffect (short effectId);
 
-            /// Remove all active effects
-            void purgeAll ();
+            /// Remove all active effects, if roll succeeds (for each effect)
+            void purgeAll (float chance);
 
             bool isSpellActive (std::string id) const;
             ///< case insensitive

apps/openmw/mwmechanics/spellcasting.cpp

@@ -236,7 +236,7 @@ namespace MWMechanics
             else if (effectId == ESM::MagicEffect::CureCorprusDisease)
                 target.getClass().getCreatureStats(target).getSpells().purgeCorprusDisease();
             else if (effectId == ESM::MagicEffect::Dispel)
-                target.getClass().getCreatureStats(target).getActiveSpells().purgeAll();
+                target.getClass().getCreatureStats(target).getActiveSpells().purgeAll(magnitude);
             else if (effectId == ESM::MagicEffect::RemoveCurse)
                 target.getClass().getCreatureStats(target).getSpells().purgeCurses();