screenshots: add better diagnostics for failing CI

Output current UI file being processed, in case any random exception
pops up.

Change-Id: If6937f70718cc801494f424f7e09e9cb8c8758f0
(cherry picked from commit fb5d849cdeebe5299da399efc9d0ca36b6fc192b)
Reviewed-on: https://gerrit.libreoffice.org/60964
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

test/source/screenshot_test.cxx

@@ -246,6 +246,8 @@ void ScreenshotTest::processDialogBatchFile(const OUString& rFile)
     const OString aComment("#");
 
     while (aStream.ReadLine(aNextUIFile))
+    {
+        try
         {
             if (!aNextUIFile.isEmpty() && !aNextUIFile.startsWith(aComment))
             {
@@ -268,6 +270,13 @@ void ScreenshotTest::processDialogBatchFile(const OUString& rFile)
                 }
             }
         }
+        catch(...)
+        {
+            OString aMsg("Exception while processing ");
+            aMsg += aNextUIFile;
+            CPPUNIT_ASSERT_MESSAGE(aMsg.getStr(), false);
+        }
+    }
 }
 
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