Update fallback revision base to zero

Changed the fallback value for the revision base to zero. The previous
value of -1 causes issues, eg, when retrieving patch set diffs in
stateful mode, as addressed in the next commit.

Fixes: 3b49995 ("Migrate GerritClientPatchSet to direct GerritApi")
Change-Id: I84bd3feb7fa2867e240071362f56751bc7e6b35f
Signed-off-by: Patrizio <patrizio.gelosi@amarulasolutions.com>

src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/common/client/api/gerrit/GerritClientPatchSet.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/common/client/api/gerrit/GerritClientPatchSet.java b/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/common/client/api/gerrit/GerritClientPatchSet.java
index c409cc5..4e17e7e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/common/client/api/gerrit/GerritClientPatchSet.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/common/client/api/gerrit/GerritClientPatchSet.java
@@ -36,7 +36,7 @@
                 Optional.ofNullable(changeInfo)
                     .map(info -> info.revisions)
                     .map(revisions -> revisions.size() - 1)
-                    .orElse(-1);
+                    .orElse(0);
         }
         catch (Exception e) {
             log.error("Could not retrieve revisions for PatchSet with fullChangeId: {}", change.getFullChangeId(), e);