font/sfnt: increase proprietary_test coverage.

Recent commits (probably 792d36e1 "support TrueType compound glyphs" and
1995ed1a "support TrueType glyph transformations") let us decode all the
glyphs in the Adobe TrueType fonts, but I forgot to update the test
coverage in those commits.

Change-Id: I7b135005cd67082f84aee16d296debdedcc9488e
Reviewed-on: https://go-review.googlesource.com/38281
Reviewed-by: David Crawshaw <crawshaw@golang.org>

font/sfnt/proprietary_test.go

diff --git a/font/sfnt/proprietary_test.go b/font/sfnt/proprietary_test.go
index e7f8fa4..f133103 100644
--- a/font/sfnt/proprietary_test.go
+++ b/font/sfnt/proprietary_test.go
@@ -84,7 +84,7 @@
 }
 
 func TestProprietaryAdobeSourceCodeProTTF(t *testing.T) {
-	testProprietary(t, "adobe", "SourceCodePro-Regular.ttf", 1500, 36)
+	testProprietary(t, "adobe", "SourceCodePro-Regular.ttf", 1500, -1)
 }
 
 func TestProprietaryAdobeSourceHanSansSC(t *testing.T) {
@@ -96,7 +96,7 @@
 }
 
 func TestProprietaryAdobeSourceSansProTTF(t *testing.T) {
-	testProprietary(t, "adobe", "SourceSansPro-Regular.ttf", 1800, 54)
+	testProprietary(t, "adobe", "SourceSansPro-Regular.ttf", 1800, -1)
 }
 
 func TestProprietaryAppleAppleSymbols(t *testing.T) {