Fix build script not working when git repo isn't cloned (#3831)

Author: JRoy

build.gradle

@@ -20,6 +20,9 @@ allprojects {
 }
 
 def commitsSinceLastTag() {
+    if (grgit == null) {
+        return 0
+    }
     def tags = grgit.tag.list().stream().map({it.commit}).toList()
     def commit = grgit.head()
     def depth = 0
@@ -32,7 +35,7 @@ def commitsSinceLastTag() {
 }
 
 ext {
-    GIT_COMMIT = grgit.head().abbreviatedId
+    GIT_COMMIT = grgit == null ? "unknown" : grgit.head().abbreviatedId
     GIT_DEPTH = commitsSinceLastTag()
 
     fullVersion = "${version}-${GIT_COMMIT}".replace("-SNAPSHOT", "-dev+${GIT_DEPTH}")