fixed lexing (syntax highlighting) of the null-character (^@) in SciTECO code

* Apparently g_utf8_get_char_validated() sometimes(!) returns -2 for null-characters,
  so it was considered an invalid byte sequence.
* What's strange and unexplainable is that other uses of the function, as are behind nA and nQq,
  did not cause problems and returned 0 for null-bytes.
* This also fixes syntax higlighting of .teco_session files which use the null-byte as the
  string terminator.
  (.teco_session files are not highlighted automatically, though.)

3 files changed, 8 insertions, 4 deletions

diff --git a/src/lexer.c b/src/lexer.c
index 4fbc313..ff43c1b 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -104,8 +104,12 @@ teco_lexer_step(teco_view_t *view, teco_machine_main_t *machine,
 
 	teco_style_t style = SCE_SCITECO_DEFAULT;
 
-	gint32 chr = g_utf8_get_char_validated(macro+machine->macro_pc,
-	                                       max_len-machine->macro_pc);
+	/*
+	 * g_utf8_get_char_validated() sometimes(?) returns -2 for "\0".
+	 */
+	gint32 chr = macro[machine->macro_pc]
+			? g_utf8_get_char_validated(macro+machine->macro_pc,
+			                            max_len-machine->macro_pc) : 0;
 	if (chr < 0) {
 		/*
 		 * Invalid UTF-8 byte sequence:
diff --git a/src/qreg.c b/src/qreg.c
index 91ee630..271e7cb 100644
--- a/src/qreg.c
+++ b/src/qreg.c
@@ -539,7 +539,7 @@ teco_qreg_external_get_character(teco_qreg_t *qreg, teco_int_t position,
 	 * The sign bit in UCS-4/UTF-32 is unused, so this will even
 	 * suffice if TECO_INTEGER == 32.
 	 */
-	*chr = (gint32)g_utf8_get_char_validated(p, -1);
+	*chr = *p ? (gint32)g_utf8_get_char_validated(p, -1) : 0;
 	return TRUE;
 }
 
diff --git a/src/view.c b/src/view.c
index 1f09ce6..b8c72a5 100644
--- a/src/view.c
+++ b/src/view.c
@@ -657,7 +657,7 @@ teco_view_get_character(teco_view_t *ctx, gsize pos, gsize len)
 	 * The sign bit in UCS-4/UTF-32 is unused, so this will even
 	 * suffice if TECO_INTEGER == 32.
 	 */
-	return (gint32)g_utf8_get_char_validated(buf, -1);
+	return *buf ? (gint32)g_utf8_get_char_validated(buf, -1) : 0;
 }
 
 void