Fix incorrect type for numeric.compound.assign when the pointer type is incompatible with the store type.

Closes #1511, #1530, #1533.

ICSharpCode.Decompiler/IL/Instructions/CompoundAssignmentInstruction.cs

@@ -97,6 +97,7 @@ namespace ICSharpCode.Decompiler.IL
 			this.AddILRange(binary);
 			Debug.Assert(compoundAssignmentType == CompoundAssignmentType.EvaluatesToNewValue || (Operator == BinaryNumericOperator.Add || Operator == BinaryNumericOperator.Sub));
 			Debug.Assert(IsValidCompoundAssignmentTarget(Target));
+			Debug.Assert(this.ResultType == (IsLifted ? StackType.O : UnderlyingResultType));
 		}
 		
 		/// <summary>

ICSharpCode.Decompiler/IL/Transforms/TransformAssignment.cs

@@ -478,9 +478,17 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				// Try to determine the real type of the object we're modifying:
 				storeType = stobj.Target.InferType(compilation);
 				if (storeType is ByReferenceType refType) {
-					storeType = refType.ElementType;
+					if (TypeUtils.IsCompatibleTypeForMemoryAccess(refType.ElementType, stobj.Type)) {
+						storeType = refType.ElementType;
+					} else {
+						storeType = stobj.Type;
+					}
 				} else if (storeType is PointerType pointerType) {
-					storeType = pointerType.ElementType;
+					if (TypeUtils.IsCompatibleTypeForMemoryAccess(pointerType.ElementType, stobj.Type)) {
+						storeType = pointerType.ElementType;
+					} else {
+						storeType = stobj.Type;
+					}
 				} else {
 					storeType = stobj.Type;
 				}