Add exception for Bulgarian to mk_hyb_file

The Bulgarian hyphenation patterns contain a line consisting of '0ь0'
which has no practical effect on hyphenation. Add an exception in
roundtrip testing to make sure we don't fail while comparing our tables
with the input data.

Test: make -j works and creates .hyb files for bg and cu
Change-Id: Ia46b8a45fe522f5194d8105d31b34b0e27528cc9
(cherry picked from commit 3e203b7b62404d3cf4aaf5e11b946047461a7a82)
diff --git a/tools/mk_hyb_file.py b/tools/mk_hyb_file.py
index 978c082..a9b8932 100755
--- a/tools/mk_hyb_file.py
+++ b/tools/mk_hyb_file.py
@@ -539,6 +539,12 @@
     patterns = []
     exceptions = []
     traverse_trie(0, '', trie_data, ch_map, pattern_data, patterns, exceptions)
+
+    # EXCEPTION for Bulgarian (bg), which contains an ineffectual line of <0, U+044C, 0>
+    if u'\u044c' in patterns:
+        patterns.remove(u'\u044c')
+        patterns.append(u'0\u044c0')
+
     assert verify_file_sorted(patterns, pat_fn), 'pattern table not verified'
     assert verify_file_sorted(exceptions, hyp_fn), 'exception table not verified'