Fix line breaking at trailing space

With a string like "abc def [inset]", it should be possible to break
between the "def" and the inset. A case of interest is when "abc def "
is too long, but "abc def" is not.

To this end, tweak the test that look whether breaking was successful:
the right width to look at is nscp_width, the width without the final
space.

src/Row.cpp

@@ -144,7 +144,7 @@ bool Row::Element::splitAt(int const width, int next_width, bool force,
                                                 isRTL(), wrap_any | force);
 
 	// if breaking did not really work, give up
-	if (!force && breaks.front().wid > width) {
+	if (!force && breaks.front().nspc_wid > width) {
 		if (dim.wid == 0)
 			dim.wid = fm.width(str);
 		return false;