DoWord adds a RuneLayout for invalid characters

Defaults to an emspace for the width. Progress on #2

layout.go

@@ -58,13 +58,16 @@ func DoWord (text []rune, face font.Face) (word WordLayout, remaining []rune) {
 		
 		// consume and process the rune
 		remaining = remaining[1:]
-		_, advance, ok := face.GlyphBounds(char)
-		if !ok { continue }
-		word.Runes = append (word.Runes, RuneLayout {
+		advance, ok := face.GlyphAdvance(char)
+		if !ok {
+			advance = tofuAdvance(face)
+		}
+		runeLayout := RuneLayout {
 			X:     x,
 			Width: advance,
 			Rune:  char,
-		})
+		}
+		word.Runes = append(word.Runes, runeLayout)
 
 		// advance
 		if gettingSpace {
@@ -209,3 +212,11 @@ func (line *LineLayout) justify () {
 		x += spacePerWord + word.Width
 	}
 }
+
+func tofuAdvance (face font.Face) fixed.Int26_6 {
+	if advance, ok := face.GlyphAdvance('M'); ok {
+		return advance
+	} else {
+		return 16
+	}
+}