git-gui: Always disable the Tcl EOF character when reading

On Windows (which includes Cygwin) Tcl defaults to leaving the EOF
character of input file streams set to the ASCII EOF character, but
if that character were to appear in the data stream then Tcl will
close the channel early.  So we have to disable eofchar on Windows.
Since the default is disabled on all platforms except Windows, we
can just disable it everywhere to prevent any sort of read problem.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/commit.tcl

@@ -209,7 +209,7 @@ A good commit message has the following format:
 	ui_status {Calling pre-commit hook...}
 	set pch_error {}
 	set fd_ph [open "| $pchook" r]
-	fconfigure $fd_ph -blocking 0 -translation binary
+	fconfigure $fd_ph -blocking 0 -translation binary -eofchar {}
 	fileevent $fd_ph readable \
 		[list commit_prehook_wait $fd_ph $curHEAD $msg]
 }