handles: panic when we cannot retrieve handle data

index.go

@@ -234,12 +234,10 @@ func (v *Index) RemoveAll(pathspecs []string, callback IndexMatchedPathCallback)
 
 //export indexMatchedPathCallback
 func indexMatchedPathCallback(cPath, cMatchedPathspec *C.char, payload unsafe.Pointer) int {
-	if payload == nil {
-		return 0
-	} else if callback, ok := pointerHandles.Get(payload).(IndexMatchedPathCallback); ok {
+	if callback, ok := pointerHandles.Get(payload).(IndexMatchedPathCallback); ok {
 		return callback(C.GoString(cPath), C.GoString(cMatchedPathspec))
 	} else {
-		return -1
+		panic("invalid matched path callback")
 	}
 }
 

submodule.go

@@ -103,7 +103,7 @@ func SubmoduleVisitor(csub unsafe.Pointer, name *C.char, handle unsafe.Pointer)
 	if callback, ok := pointerHandles.Get(handle).(SubmoduleCbk); ok {
 		return (C.int)(callback(sub, C.GoString(name)))
 	} else {
-		return -1
+		panic("invalid submodule visitor callback")
 	}
 }
 

tree.go

@@ -97,7 +97,7 @@ func CallbackGitTreeWalk(_root unsafe.Pointer, _entry unsafe.Pointer, ptr unsafe
 	if callback, ok := pointerHandles.Get(ptr).(TreeWalkCallback); ok {
 		return C.int(callback(root, newTreeEntry(entry)))
 	} else {
-		return C.int(-1)
+		panic("invalid treewalk callback")
 	}
 }