Fix the issue of going out of bounds in the isccfg parser.

This problem can occur when attempting to parse an empty file.

repos/system_upgrade/el7toel8/libraries/isccfg.py

@@ -688,9 +688,12 @@ def find_next_key(self, cfg, index=0, end_index=-1, end_report=False):
 
         while index != -1:
             keystart = index
-            while istr[index] in self.CHAR_KEYWORD and index < end_index:
+            while index < end_index and istr[index] in self.CHAR_KEYWORD:
                 index += 1
 
+            if index >= end_index:
+                break
+
             if keystart < index <= end_index and istr[index] not in self.CHAR_KEYWORD:
                 # key has been found
                 return ConfigSection(cfg, istr[keystart:index], keystart, index-1)

repos/system_upgrade/el7toel8/libraries/tests/test_isccfg.py

@@ -116,6 +116,10 @@
 };
 """)
 
+config_empty = isccfg.MockConfig('')
+
+config_empty_include = isccfg.MockConfig('options { include "/dev/null"; };')
+
 
 def check_in_section(parser, section, key, value):
     """ Helper to check some section was found
@@ -343,5 +347,33 @@ def test_walk():
     assert 'dnssec-validation' not in state
 
 
+def test_empty_config():
+    """ Test empty configuration """
+
+    callbacks = {}
+
+    parser = isccfg.IscConfigParser(config_empty)
+    assert len(parser.FILES_TO_CHECK) == 1
+    cfg = parser.FILES_TO_CHECK[0]
+    parser.walk(cfg.root_section(), callbacks)
+    assert cfg.buffer == ''
+
+
+def test_empty_include_config():
+    """ Test empty configuration """
+
+    callbacks = {}
+
+    parser = isccfg.IscConfigParser(config_empty_include)
+    assert len(parser.FILES_TO_CHECK) == 2
+    cfg = parser.FILES_TO_CHECK[0]
+    parser.walk(cfg.root_section(), callbacks)
+    assert cfg.buffer == 'options { include "/dev/null"; };'
+
+    null_cfg = parser.FILES_TO_CHECK[1]
+    parser.walk(null_cfg.root_section(), callbacks)
+    assert null_cfg.buffer == ''
+
+
 if __name__ == '__main__':
     test_key_views_lookaside()