Don't map glyphs to the Lepcha Unicode block (issue 7426)

In the PDF file in the issue, some of the glyphs end up being mapped to the Lepcha Unicode block; see https://en.wikipedia.org/wiki/Lepcha_(Unicode_block).
This didn't use to matter, but after HarfBuzz updates that improved support for Lepcha fonts, in particular https://bugzilla.mozilla.org/show_bug.cgi?id=1249861, some glyphs are now moved horizontally.
To avoid that, this patch adds the Lepcha block to the list of Unicode ranges that we skip when building the glyph mapping.

Fixes 7426.

test/pdfs/.gitignore

@@ -27,6 +27,7 @@
 !issue7180.pdf
 !issue7200.pdf
 !issue7229.pdf
+!issue7426.pdf
 !issue7439.pdf
 !filled-background.pdf
 !ArabicCIDTrueType.pdf

test/test_manifest.json

@@ -1701,6 +1701,13 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "issue7426",
+       "file": "pdfs/issue7426.pdf",
+       "md5": "304e6cae18fdc07f66bd621fbe16b6cb",
+       "link": false,
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue6782",
        "file": "pdfs/issue6782.pdf",
        "md5": "b423f709600daa5745cc6d8234f7c608",