Don't allow '_' in first place of version code

Fixes a regression of 2cb0ff45. Example:

versionCode project.versionCode_plus

931b0a3087/app/build.gradle (L38)

fdroidserver/common.py

@@ -1579,7 +1579,7 @@ def remove_debuggable_flags(root_dir):
                         os.path.join(root, 'AndroidManifest.xml'))
 
 
-vcsearch_g = re.compile(r'''\b[Vv]ersionCode\s*=?\s*["'(]*([0-9_]+)["')]*''').search
+vcsearch_g = re.compile(r'''\b[Vv]ersionCode\s*=?\s*["'(]*([0-9][0-9_]*)["')]*''').search
 vnsearch_g = re.compile(r'''\b[Vv]ersionName\s*=?\s*\(?(["'])((?:(?=(\\?))\3.)*?)\1''').search
 vnssearch_g = re.compile(r'''\b[Vv]ersionNameSuffix\s*=?\s*(["'])((?:(?=(\\?))\3.)*?)\1''').search
 psearch_g = re.compile(r'''\b(packageName|applicationId)\s*=*\s*["']([^"']+)["']''').search

tests/common.TestCase

@@ -1222,6 +1222,19 @@ class CommonTest(unittest.TestCase):
         self.assertEqual(('20180430-underscore', '2018_04_30', 'com.kunzisoft.fdroidtest.applicationidsuffix.underscore'),
                          fdroidserver.common.parse_androidmanifests(paths, app))
 
+        app = fdroidserver.metadata.App()
+        build = fdroidserver.metadata.Build()
+        build.gradle = ['underscore_first']
+        app['Builds'] = [build]
+        app.id = 'com.kunzisoft.fdroidtest.applicationidsuffix.underscore_first'
+        paths = [
+            os.path.join('source-files', 'com.kunzisoft.testcase', 'build.gradle'),
+        ]
+        for path in paths:
+            self.assertTrue(os.path.isfile(path))
+        self.assertEqual(('1.0', '1', 'com.kunzisoft.fdroidtest.applicationidsuffix.underscore_first'),
+                         fdroidserver.common.parse_androidmanifests(paths, app))
+
     def test_get_all_gradle_and_manifests(self):
         """Test whether the function works with relative and absolute paths"""
         a = fdroidserver.common.get_all_gradle_and_manifests(Path('source-files/cn.wildfirechat.chat'))

tests/source-files/com.kunzisoft.testcase/build.gradle

@@ -59,6 +59,15 @@ android {
             // Version code : 2018_04_30
             // Version name : 20180430-underscore
         }
+        underscore_first {
+            applicationIdSuffix = ".underscore_first"
+            versionCode _04_30
+            buildConfigField "boolean", "FULL_VERSION", "true"
+            buildConfigField "boolean", "CLOSED_STORE", "true"
+            // ApplicationId : com.kunzisoft.fdroidtest.applicationidsuffix.underscore_first
+            // Version code : 1
+            // Version name : 1.0
+        }
     }
 }