fix(java): skip fixing poms for special modules (#1744) (#299)

fix(java): handle empty modules

Fixes googleapis/synthtool#1743
Source-Link: googleapis/synthtool@482d649
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:bd5071596a47614d1fe15eb766c4255bae330f823b606e1196a3b0c8d2e96fd1

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: losalex <90795544+losalex@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -13,5 +13,4 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:d5da32501662e4e53365220cc14cfb1d3b9446585397d57dac50171d92556ae7
-
+  digest: sha256:bd5071596a47614d1fe15eb766c4255bae330f823b606e1196a3b0c8d2e96fd1