`ArrayIndexOutOfBoundsException` for specific invalid content, with Reader-based parser

[cowtowncoder]

(note: found by OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=61198)

Looks like there is a case where, if:

1. JsonParser configured to accept non-standard leading plus sign (JsonReadFeature.ALLOW_LEADING_PLUS_SIGN_FOR_NUMBERS)
2. Content is read using character-based parser (ReaderBasedJsonParser)
3. Some boundary condition is reached (can emulate with 1-char-at-a-time Reader)
4. Call is made to JsonParser.getNumberType() (or possibly other number accessors)

there's an AIOOBE with stack trace like:

 	 at com.fasterxml.jackson.core.io.NumberInput.parseInt(NumberInput.java:55)
	 at com.fasterxml.jackson.core.util.TextBuffer.contentsAsInt(TextBuffer.java:631)
	 at com.fasterxml.jackson.core.base.ParserBase._parseNumericValue(ParserBase.java:891)
	 at com.fasterxml.jackson.core.base.ParserBase.getNumberType(ParserBase.java:735)