Fix panic in TextMBB for empty message

Signed-off-by: Glenn Lewis <[email protected]>

Author: gmlewis

fonts/freeserif/font_test.go

@@ -0,0 +1,14 @@
+package freeserif
+
+import (
+	"testing"
+
+	"github.com/gmlewis/go-fonts/fonts"
+)
+
+func TestTextMBB(t *testing.T) {
+	// See: https://github.com/gmlewis/go-gerber/issues/8
+	if _, err := fonts.TextMBB(0, 0, 1, 1, "", "freeserif"); err == nil {
+		t.Error("TextMBB = nil, want err")
+	}
+}

fonts/text.go

@@ -187,6 +187,10 @@ func TextMBB(xPos, yPos, xScale, yScale float64, message, fontName string) (*MBB
 		}
 	}
 
+	if result == nil {
+		return nil, errors.New("message must not be empty")
+	}
+
 	// log.Printf("TextMBB: xScale,yScale=(%v,%v)", xScale, yScale)
 	fsf := 1.0 / font.UnitsPerEm
 	xScale *= fsf