fix(forms): use expression form for conditional fieldError reset

Vue template attribute expressions don't allow if-statements; the
short-circuit form (`x && (x = '')`) is the idiomatic equivalent and
runs without a template compiler warning.

app/pages/accept-invite.vue

@@ -33,7 +33,7 @@
               type="text"
               required
               @blur="validateName"
-              @input="if (fieldErrors.name) fieldErrors.name = ''"
+              @input="fieldErrors.name && (fieldErrors.name = '')"
             >
             <p v-if="fieldErrors.name" class="field-error">{{ fieldErrors.name }}</p>
           </div>

app/pages/join.vue

@@ -129,7 +129,7 @@
                   type="text"
                   required
                   @blur="validateName"
-                  @input="if (fieldErrors.name) fieldErrors.name = ''"
+                  @input="fieldErrors.name && (fieldErrors.name = '')"
                 >
                 <p v-if="fieldErrors.name" class="field-error">{{ fieldErrors.name }}</p>
               </div>
@@ -143,7 +143,7 @@
                   placeholder="you@example.com"
                   required
                   @blur="validateEmail"
-                  @input="if (fieldErrors.email) fieldErrors.email = ''"
+                  @input="fieldErrors.email && (fieldErrors.email = '')"
                 >
                 <p v-if="fieldErrors.email" class="field-error">{{ fieldErrors.email }}</p>
               </div>

app/pages/member/account.vue

@@ -174,7 +174,7 @@
                     placeholder="you@example.com"
                     autofocus
                     @blur="validateNewEmail"
-                    @input="if (fieldErrors.email) fieldErrors.email = ''"
+                    @input="fieldErrors.email && (fieldErrors.email = '')"
                     @keydown.enter="handleUpdateEmail"
                     @keydown.escape="cancelEmailEdit"
                   >