Consume the current character when encountering illegal characters in Lexer.getObject, in order to prevent infinite loops during reading of streams (issue 8061)

*Please note:* The rendering of the PDF file in issue 8061 first regressed in PR 7039, and then PR 7493 exacerbated the problem even further by causing an infinite loop.

In this particular case, when errors were encountered inside of the `Lexer.getObject` method *itself*, we didn't advance the stream position. This thus caused an inifinite loop in `parseCMap`, since the exact same character was then parsed over and over again.

Fixes 8061.

test/pdfs/.gitignore

@@ -45,6 +45,7 @@
 !issue7855.pdf
 !issue7872.pdf
 !issue7901.pdf
+!issue8061.pdf
 !bad-PageLabels.pdf
 !filled-background.pdf
 !ArabicCIDTrueType.pdf

test/test_manifest.json

@@ -1712,6 +1712,13 @@
        "link": false,
        "type": "eq"
     },
+    {  "id": "issue8061",
+       "file": "pdfs/issue8061.pdf",
+       "md5": "d61fe1dcdcd55bca00b351b2fc2c6dc7",
+       "rounds": 1,
+       "link": false,
+       "type": "eq"
+    },
     {  "id": "issue7580-eq",
        "file": "pdfs/issue7580.pdf",
        "md5": "44dd5a9b4373fcab9890cf567722a766",