Fix failure in printing/BUILD.gn when not using a sysroot. Without this change, gn gen fails with "…

printing/cups_config_helper.py

Index: printing/cups_config_helper.py
diff --git a/printing/cups_config_helper.py b/printing/cups_config_helper.py
index 138a688735a1e0c35919357d3cefd6a44fd2e753..95383cf2fd426cccbd9f6a5df5a9c6df680ee17f 100755
--- a/printing/cups_config_helper.py
+++ b/printing/cups_config_helper.py
@@ -63,7 +63,7 @@ def main():
     return 1
 
   mode = sys.argv[1]
-  if len(sys.argv) > 2:
+  if len(sys.argv) > 2 and sys.argv[2]:
     sysroot = sys.argv[2]
     cups_config = os.path.join(sysroot, 'usr', 'bin', 'cups-config')
     if not os.path.exists(cups_config):