Don't show red X for labels with min value 0

If a label's minimum value is 0, use blank/check instead of X/check. A
red X feels like a reviewer has actively done something to reject the
change, but this is not the case; it's just a missing approval.

Don't apply the converse when the maximum value is 0; a check mark by
default is less jarring than an X by default.

Change-Id: I03f53367a47e53373d03efaa0fb07b5c7d9f6335

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ApprovalTable.java

@@ -224,7 +224,7 @@ public class ApprovalTable extends Composite {
             String fv = formatValue(ai.value());
             if (fv.equals(max)) {
               ad.approved(name);
-            } else if (fv.equals(min)) {
+            } else if (ai.value() < 0 && fv.equals(min)) {
               ad.rejected(name);
             }
           }