Fix T61759: Dynamic paint smudge crash

The issue was caused by mesh needed for dynamic paint brush being
stored in the modifier. That make it to be freed and set to NULL
when running copy-on-write.

Solved by moving the mesh to be stored in modifier's runtime data.

source/blender/modifiers/intern/MOD_dynamicpaint.c

@@ -58,6 +58,15 @@ static void copyData(const ModifierData *md, ModifierData *target, const int fla
 	dynamicPaint_Modifier_copy(pmd, tpmd, flag);
 }
 
+static void freeRuntimeData(void *runtime_data_v)
+{
+	if (runtime_data_v == NULL) {
+		return;
+	}
+	DynamicPaintRuntime *runtime_data = (DynamicPaintRuntime *)runtime_data_v;
+	dynamicPaint_Modifier_free_runtime(runtime_data);
+}
+
 static void freeData(ModifierData *md)
 {
 	DynamicPaintModifierData *pmd = (DynamicPaintModifierData *) md;
@@ -192,5 +201,5 @@ ModifierTypeInfo modifierType_DynamicPaint = {
 	/* foreachObjectLink */ NULL,
 	/* foreachIDLink */     foreachIDLink,
 	/* foreachTexLink */    foreachTexLink,
-	/* freeRuntimeData */   NULL,
+	/* freeRuntimeData */   freeRuntimeData,
 };