giscanner: Don't run pkg-config when there's no packages specified

This prevents a simple error from pkg-config, "Must specify package names
on command line"

https://bugzilla.gnome.org/show_bug.cgi?id=673668

diff --git a/giscanner/scannermain.py b/giscanner/scannermain.py
index bcacd0f..794cede 100755 (executable)
--- a/giscanner/scannermain.py
+++ b/giscanner/scannermain.py
@@ -405,9 +405,10 @@ def scanner_main(args):
 
     packages = set(options.packages)
     packages.update(transformer.get_pkgconfig_packages())
-    exit_code = process_packages(options, packages)
-    if exit_code:
-        return exit_code
+    if packages:
+        exit_code = process_packages(options, packages)
+        if exit_code:
+            return exit_code
 
     ss = create_source_scanner(options, args)