fix(systemtags): ensure no invalid color is passed to NcColorPicker

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

Author: susnux

apps/systemtags/src/components/SystemTagPicker.vue

@@ -51,7 +51,7 @@
 					<!-- Color picker -->
 					<NcColorPicker v-if="canEditOrCreateTag"
 						:data-cy-systemtags-picker-tag-color="tag.id"
-						:value="`#${tag.color}`"
+						:value="`#${tag.color || '000000'}`"
 						:shown="openedPicker === tag.id"
 						class="systemtags-picker__tag-color"
 						@update:value="onColorChange(tag, $event)"