fix(core): fix move down throw errors and fix null assign merge throw errors (#961)

Author: janryWang

packages/core/src/externals.ts

@@ -1041,7 +1041,7 @@ export const createFormExternals = (
       },
       moveDown(index: number) {
         const len = toArr(getValue()).length
-        return mutators.move(index, index + 1 > len ? 0 : index + 1)
+        return mutators.move(index, index + 1 >= len ? 0 : index + 1)
       },
       validate(opts?: IFormExtendedValidateFieldOptions) {
         return validate(

packages/shared/src/merge.ts

@@ -90,8 +90,8 @@ function propertyIsUnsafe(target, key) {
 
 function mergeObject(target: any, source: any, options: Options) {
   const destination = options.assign ? target : {}
-
-  if (!options.assign && options.isMergeableObject(target)) {
+  if (!options.isMergeableObject(target)) return target
+  if (!options.assign) {
     getKeys(target).forEach(function(key) {
       destination[key] = cloneUnlessOtherwiseSpecified(target[key], options)
     })