Fix bug with diff context 0

In past, it was possible to set context 0. Currently context 0 was
overriden by default context (10). This change enables context 0 and
it uses it for diff for user suggested edits.

Release-Notes: skip
Google-Bug-Id: b/277102018
Change-Id: I3af90d12f4f2dca1859dffcd3a31654dab726c03
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
index c41dc91..7e30581 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
@@ -226,7 +226,7 @@
     return FULL_CONTEXT;
   }
   if (
-    prefsContext &&
+    prefsContext !== undefined &&
     !(showFullContext === FullContext.NO && prefsContext === FULL_CONTEXT)
   ) {
     return prefsContext;