inputw: improve correctness and startup performance

a massive amount of time inside readstdin() is spent trying to get the
max input width and then put it into inputw, only for it to get clamped
down to mw/3 inside setup().

it makes more sense to calculate inputw inside setup() once we have mw
available. similar to the last patch, i see noticeable startup
performance improvement:

before -> after
160ms  -> 60ms

additionally this will take fallback fonts into account compared to the
previous version, so it's not only more performant but also more correct.

dmenu.c

@@ -547,8 +547,7 @@ static void
 readstdin(void)
 {
 	char buf[sizeof text], *p;
-	size_t i, imax = 0, size = 0;
-	unsigned int tmpmax = 0;
+	size_t i, size = 0;
 
 	/* read each line from stdin and add it to the item list */
 	for (i = 0; fgets(buf, sizeof buf, stdin); i++) {
@@ -560,15 +559,9 @@ readstdin(void)
 		if (!(items[i].text = strdup(buf)))
 			die("cannot strdup %u bytes:", strlen(buf) + 1);
 		items[i].out = 0;
-		drw_font_getexts(drw->fonts, buf, strlen(buf), &tmpmax, NULL);
-		if (tmpmax > inputw) {
-			inputw = tmpmax;
-			imax = i;
-		}
 	}
 	if (items)
 		items[i].text = NULL;
-	inputw = items ? TEXTW(items[imax].text) : 0;
 	lines = MIN(lines, i);
 }
 
@@ -614,12 +607,13 @@ static void
 setup(void)
 {
 	int x, y, i, j;
-	unsigned int du;
+	unsigned int du, tmp;
 	XSetWindowAttributes swa;
 	XIM xim;
 	Window w, dw, *dws;
 	XWindowAttributes wa;
 	XClassHint ch = {"dmenu", "dmenu"};
+	struct item *item;
 #ifdef XINERAMA
 	XineramaScreenInfo *info;
 	Window pw;
@@ -677,7 +671,12 @@ setup(void)
 		mw = wa.width;
 	}
 	promptw = (prompt && *prompt) ? TEXTW(prompt) - lrpad / 4 : 0;
-	inputw = MIN(inputw, mw/3);
+	for (item = items; item && item->text; ++item) {
+		if ((tmp = textw_clamp(item->text, mw/3)) > inputw) {
+			if ((inputw = tmp) == mw/3)
+				break;
+		}
+	}
 	match();
 
 	/* create menu window */