test-setup.sh: don't cat the log file if it does not exists

This should fix flakiness of test_flaky_test

PiperOrigin-RevId: 164467764
diff --git a/tools/test/test-setup.sh b/tools/test/test-setup.sh
index 896998f..18796c3 100755
--- a/tools/test/test-setup.sh
+++ b/tools/test/test-setup.sh
@@ -141,10 +141,12 @@
 fi
 
 function encode_output_file {
-  # Replace invalid XML characters and invalid sequence in CDATA
-  # cf. https://stackoverflow.com/a/7774512/4717701
-  perl -CSDA -pe's/[^\x9\xA\xD\x20-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]+/?/g;' "$1" \
-    | sed 's|]]>|]]>]]<![CDATA[>|g'
+  if [ -f "$1" ]; then
+    # Replace invalid XML characters and invalid sequence in CDATA
+    # cf. https://stackoverflow.com/a/7774512/4717701
+    perl -CSDA -pe's/[^\x9\xA\xD\x20-\x{D7FF}\x{E000}-\x{FFFD}\x{10000}-\x{10FFFF}]+/?/g;' "$1" \
+      | sed 's|]]>|]]>]]<![CDATA[>|g'
+  fi
 }
 
 function write_xml_output_file {