Return after 'reject' in Promise constructor

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) => {