Fix bug with empty inc and exc
This fixes an exception that showed up when importing patches
+ hg init
+ hg add file1 file2
+ hg commit -m added file1 and file2 -d 0 0 -u user
+ hg commit -m changed file1 -d 0 0 -u user
+ hg -q log
1:f4d7a8c73d231bc078e2a5e791325e55e8a4c252
0:232e179b3f294d467cfa66e1439bc5b0d44e4a93
+ hg id
f4d7a8c73d23 tip
+ hg update -C 0
+ hg id
232e179b3f29
+ hg id
232e179b3f29+
+ hg revert
+ hg diff
+ hg status
+ hg id
232e179b3f29
+ hg update
+ hg diff
+ hg status
+ hg id
f4d7a8c73d23 tip
+ hg update -C 0
+ hg update
merge: warning: conflicts during merge
merging file1
merging file1 failed!
+ hg diff
diff -r f4d7a8c73d23 file1
--- a/file1
+++ b/file1
@@ -1,3 +1,7 @@
added file1
another line of text
+<<<<<<<
+changed file1 different
+=======
changed file1
+>>>>>>>
+ hg status
M file1
+ hg id
f4d7a8c73d23+ tip
+ hg revert
+ hg diff
+ hg status
+ hg id
f4d7a8c73d23 tip
+ hg revert -r tip
+ hg diff
+ hg status
+ hg id
f4d7a8c73d23 tip
+ hg update -C
+ hg diff
+ hg status
+ hg id
f4d7a8c73d23 tip