mandoc: Fix a bug in .Ql handling that has been present since the

[schwarze@mandoc.bsd.lv]

Log Message:
-----------
Fix a bug in .Ql handling that has been present since the beginning (2017).

Since the .Ql macro action uses an output prefix of "'`" and an output
suffix of "`'", md_post_raw() would decrement the code_blocks state variable 
even though md_pre_raw() had earlier neglected to increment it, hence
leaving the variable in an invalid negative state.  That in turn could
result in corrupt output in a variety of ways.

Fix this by checking in md_pre_raw() whether the prefix *contains* a
backtick rather than only checking whether it *starts* with a backtick.
For consistency, apply the same change to md_post_raw() even though 
there was no bug in that function: all *suffixes* containing a backtick
actually contain it in the leading position.

Thanks to job@ for reporting this bug.  He noticed a particularly nasty
kind of output corruption: having .Ql in an input file would result
in ASCII_NBRSP (0x31) sneaking through into the output stream if later,
unrelated parts of the same input file directly or indirectly used 
the \~ escape sequence, for example by using the .Ex macro.

Modified Files:
--------------
    mandoc:
        mdoc_markdown.c

Revision Data
-------------
Index: mdoc_markdown.c
===================================================================
RCS file: /home/cvs/mandoc/mandoc/mdoc_markdown.c,v
diff -Lmdoc_markdown.c -Lmdoc_markdown.c -u -p -r1.37 -r1.38
--- mdoc_markdown.c
+++ mdoc_markdown.c
@@ -750,7 +750,7 @@ md_pre_raw(struct roff_node *n)
 	if ((prefix = md_act(n->tok)->prefix) != NULL) {
 		md_rawword(prefix);
 		outflags &= ~MD_spc;
-		if (*prefix == '`')
+		if (strchr(prefix, '`') != NULL)
 			code_blocks++;
 	}
 	return 1;
@@ -764,7 +764,7 @@ md_post_raw(struct roff_node *n)
 	if ((suffix = md_act(n->tok)->suffix) != NULL) {
 		outflags &= ~(MD_spc | MD_nl);
 		md_rawword(suffix);
-		if (*suffix == '`')
+		if (strchr(suffix, '`') != NULL)
 			code_blocks--;
 	}
 }
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