Validate hex colors when creating/editing labels

Author: kemzeb

templates/repo/issue/labels/label_edit_modal.tmpl

@@ -50,7 +50,7 @@
 			<div class="field">
 				<label for="color">{{ctx.Locale.Tr "repo.issues.label_color"}}</label>
 				<div class="column js-color-picker-input">
-					<input name="color" value="#70c24a" placeholder="#c320f6" required maxlength="7">
+					<input name="color" value="#70c24a" placeholder="#c320f6" required pattern="^#?[A-Fa-f0-9]+$" maxlength="7">
 					{{template "repo/issue/label_precolors"}}
 				</div>
 			</div>