update: fix running without androguard

Soon, we can rip out all the aapt parsing stuff, but not yet!

fdroidserver/common.py

@@ -2528,7 +2528,7 @@ def get_first_signer_certificate(apkpath):
         elif len(cert_files) == 1:
             cert_encoded = get_certificate(apk.read(cert_files[0]))
 
-    if not cert_encoded:
+    if not cert_encoded and use_androguard():
         apkobject = _get_androguard_APK(apkpath)
         certs = apkobject.get_certificates_der_v2()
         if len(certs) > 0:

tests/update.TestCase

@@ -255,9 +255,13 @@ class UpdateTest(unittest.TestCase):
         self.assertEqual(good_fingerprint, sig,
                          'python sig was: ' + str(sig))
         # check that v1 and v2 have the same certificate
-        import hashlib
-        from binascii import hexlify
-        from androguard.core.bytecodes.apk import APK
+        try:
+            import hashlib
+            from binascii import hexlify
+            from androguard.core.bytecodes.apk import APK
+        except ImportError:
+            print('WARNING: skipping rest of test since androguard is missing!')
+            return
         apkobject = APK(apkpath)
         cert_encoded = apkobject.get_certificates_der_v2()[0]
         self.assertEqual(good_fingerprint, sig,