The --why parameter in whichgit should be optional

Test: ./build/make/tools/whichgit --modules out/target/product/coral/system.img
Change-Id: Ibc6e208d75c8e68c8130dc9ba3fc7af51390691b
diff --git a/tools/whichgit b/tools/whichgit
index 24d6d87..b0bf2e4 100755
--- a/tools/whichgit
+++ b/tools/whichgit
@@ -95,11 +95,12 @@
   # Print the list of git directories that has one or more of the sources in it
   for project in sorted(get_referenced_projects(get_git_dirs(), sources)):
     print(project)
-    if "*" in args.why or project in args.why:
-      prefix = project + "/"
-      for f in sources:
-        if f.startswith(prefix):
-          print("  " + f)
+    if args.why:
+      if "*" in args.why or project in args.why:
+        prefix = project + "/"
+        for f in sources:
+          if f.startswith(prefix):
+            print("  " + f)
 
 
 if __name__ == "__main__":