fix(format): Never disable undo button

Fix issue when undo format can be disabled if there are no format issues.

Change-Id: Iff5168d58eeb89732975ccecca4417b96f5fc72f
Release-Notes: skip
Signed-off-by: Milutin Kristofic <milutin@google.com>
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
index 4f9f751..48366a3 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
@@ -405,7 +405,7 @@
                 link
                 class="format-button"
                 @click=${this.handleFormat}
-                ?disabled=${this.formatDisabled}
+                ?disabled=${this.formatDisabled && !this.lastFormattedContent}
                 .title=${this.computeFormatButtonTooltip(
                   this.formatDisabled,
                   this.formattedErrors,