Fix failed media uploads bricking the frontend

The upload call hid errors and the entity normaliser lets them pass
through as well (assuming it must be an already "correctly" formatted
legacy qvitter response), which led to errors being added to the the
draft as if it was a valid attachment object.
On later use of this error exceptions occur breaking the frontend and
due to being saved as part of a draft this could only be recovered by
clearing local client data.

Fixes: #339

src/components/media_upload/media_upload.js

@@ -42,8 +42,14 @@ const mediaUpload = {
         .then((fileData) => {
           self.$emit('uploaded', fileData)
           self.decreaseUploadCount()
-        }, (error) => {  
-          self.$emit('upload-failed', 'default')
+        }, (error) => {
+          var msg = typeof error === "string" ? error : error.message
+          if (msg) {
+            self.$emit('upload-failed', 'message', [msg])
+          } else {
+            self.$emit('upload-failed', 'default')
+          }
+          console.warn(`Failed to upload media: ${error}`)
           self.decreaseUploadCount()
         })
     },

src/services/api/api.service.js

@@ -124,6 +124,21 @@ let fetch = (url, options) => {
   return oldfetch(fullUrl, options)
 }
 
+// TOOD: check if it is safe for all fetch() calls and can be directly integrated above
+const getJsonIfSuccess = (response, url, options) => {
+  return new Promise((resolve, reject) => response.json()
+    .then((json) => {
+      if (!response.ok) {
+        return reject(new StatusCodeError(response.status, json, { url, options }, response))
+      }
+      return resolve(json)
+    })
+    .catch((error) => {
+      return reject(new StatusCodeError(response.status, error, { url, options }, response))
+    })
+  )
+}
+
 const promisedRequest = ({ method, url, params, payload, credentials, headers = {} }) => {
   const options = {
     method,
@@ -148,19 +163,7 @@ const promisedRequest = ({ method, url, params, payload, credentials, headers =
     }
   }
   return fetch(url, options)
-    .then((response) => {
-      return new Promise((resolve, reject) => response.json()
-        .then((json) => {
-          if (!response.ok) {
-            return reject(new StatusCodeError(response.status, json, { url, options }, response))
-          }
-          return resolve(json)
-        })
-        .catch((error) => {
-          return reject(new StatusCodeError(response.status, error, { url, options }, response))
-        })
-      )
-    })
+    .then((response) => getJsonIfSuccess(response))
 }
 
 const updateNotificationSettings = ({ credentials, settings }) => {
@@ -988,7 +991,7 @@ const uploadMedia = ({ formData, credentials }) => {
     method: 'POST',
     headers: authHeaders(credentials)
   })
-    .then((data) => data.json())
+    .then((response) => getJsonIfSuccess(response, MASTODON_MEDIA_UPLOAD_URL, {}))
     .then((data) => parseAttachment(data))
 }