do not fail if git info cannot be retrieved

fixes #2785

Author: Vladimir Kotal

opengrok-indexer/pom.xml

@@ -210,6 +210,7 @@ Portions Copyright (c) 2017-2018, Chris Fraire <[email protected]>.
                     <includeOnlyProperties>
                         <includeOnlyProperty>^git.commit.id</includeOnlyProperty>
                     </includeOnlyProperties>
+		    <failOnNoGitDirectory>false</failOnNoGitDirectory>
                 </configuration>
                 <executions>
                     <execution>