Return after 'reject' in Promise constructor (#8857)

There were three cases where execution unintentionally continued after
an error was encountered. These cases likely are impossible to
encounter in practice due to recent validation improvements in the
`eth-json-rpc-middleware/wallet` module, but they were broken
nonetheless.

Execution inside the Promise constructor now halts immediately after
`reject` is called.

app/scripts/lib/decrypt-message-manager.js

@@ -82,7 +82,7 @@ export default class DecryptMessageManager extends EventEmitter {
   addUnapprovedMessageAsync (msgParams, req) {
     return new Promise((resolve, reject) => {
       if (!msgParams.from) {
-        reject(new Error('MetaMask Decryption: from field is required.'))
+        return reject(new Error('MetaMask Decryption: from field is required.'))
       }
       const msgId = this.addUnapprovedMessage(msgParams, req)
       this.once(`${msgId}:finished`, (data) => {

app/scripts/lib/encryption-public-key-manager.js

@@ -79,7 +79,7 @@ export default class EncryptionPublicKeyManager extends EventEmitter {
   addUnapprovedMessageAsync (address, req) {
     return new Promise((resolve, reject) => {
       if (!address) {
-        reject(new Error('MetaMask Message: address field is required.'))
+        return reject(new Error('MetaMask Message: address field is required.'))
       }
       const msgId = this.addUnapprovedMessage(address, req)
       this.once(`${msgId}:finished`, (data) => {

app/scripts/lib/personal-message-manager.js

@@ -85,7 +85,7 @@ export default class PersonalMessageManager extends EventEmitter {
   addUnapprovedMessageAsync (msgParams, req) {
     return new Promise((resolve, reject) => {
       if (!msgParams.from) {
-        reject(new Error('MetaMask Message Signature: from field is required.'))
+        return reject(new Error('MetaMask Message Signature: from field is required.'))
       }
       const msgId = this.addUnapprovedMessage(msgParams, req)
       this.once(`${msgId}:finished`, (data) => {