tweaks: elide a function from a non-UTF8 build

In a non-UTF8 build, mbwidth() returns always 1, so it is pointless
to call that function and compare its result to zero then.

Also, don't bother special-casing the function for a non-UTF8 locale.

src/chars.c

@@ -200,11 +200,10 @@ char control_mbrep(const char *c, bool isdata)
 		return control_rep(*c);
 }
 
+#ifdef ENABLE_UTF8
 /* This function is equivalent to wcwidth() for multibyte characters. */
 int mbwidth(const char *c)
 {
-#ifdef ENABLE_UTF8
-	if (use_utf8) {
 		wchar_t wc;
 		int width;
 
@@ -213,14 +212,12 @@ int mbwidth(const char *c)
 
 		width = wcwidth(wc);
 
-		if (width == -1)
+		if (width < 0)
 			return 1;
 
 		return width;
-	} else
-#endif
-		return 1;
 }
+#endif
 
 /* Convert the Unicode value in code to a multibyte character, if possible.
  * If the conversion succeeds, return the (dynamically allocated) multibyte

src/proto.h

@@ -213,7 +213,9 @@ bool is_ascii_cntrl_char(int c);
 bool is_cntrl_mbchar(const char *c);
 bool is_word_mbchar(const char *c, bool allow_punct);
 char control_mbrep(const char *c, bool isdata);
+#ifdef ENABLE_UTF8
 int mbwidth(const char *c);
+#endif
 char *make_mbchar(long chr, int *chr_mb_len);
 int char_length(const char *pointer);
 int parse_mbchar(const char *buf, char *chr, size_t *col);

src/winio.c

@@ -1890,11 +1890,13 @@ char *display_string(const char *buf, size_t column, size_t span,
 
 #ifdef ENABLE_UTF8
 #define ISO8859_CHAR  FALSE
+#define ZEROWIDTH_CHAR  (mbwidth(buf) == 0)
 #else
 #define ISO8859_CHAR  ((unsigned char)*buf > 0x9F)
+#define ZEROWIDTH_CHAR  FALSE
 #endif
 
-	while (*buf != '\0' && (column < beyond || mbwidth(buf) == 0)) {
+	while (*buf != '\0' && (column < beyond || ZEROWIDTH_CHAR)) {
 		/* A plain printable ASCII character is one byte, one column. */
 		if (((signed char)*buf > 0x20 && *buf != DEL_CODE) || ISO8859_CHAR) {
 			converted[index++] = *(buf++);
@@ -1983,14 +1985,16 @@ char *display_string(const char *buf, size_t column, size_t span,
 	/* If there is more text than can be shown, make room for the ">". */
 	if (column > beyond || (*buf != '\0' && (isprompt ||
 					(isdata && !ISSET(SOFTWRAP))))) {
+#ifdef ENABLE_UTF8
 		do {
 			index = step_left(converted, index);
 		} while (mbwidth(converted + index) == 0);
 
-#ifdef ENABLE_UTF8
 		/* Display the left half of a two-column character as '['. */
 		if (mbwidth(converted + index) == 2)
 			converted[index++] = '[';
+#else
+		index--;
 #endif
 	}