OpenSystemsDevelopment / qpdf

...as well as some cases generated in CI from earlier attempts at
fixing this.

A parse error in stream data in which stream data contained a nested
object would cause a crash because qpdf was not correctly updating its
internal state. Rework the QPDF json reactor to not be sensitive to
parse errors in this way.

Allow "n:/pdf-syntax" JSON syntax for dictionary keys

Update TODO.md regarding indirect nulls in QPDF_Dictionary

Also, modernize for loop.

Instead of overwriting cur_row.data() use clear and insert.

Tighten checks for invalid indirect references  during xref reconstru…

Handle default-constructed JSON objects

Tighten checks for invalid indirect references in QPDFParser

Update .clang-format to require braces after control statements

Fix incorrect handling of invalid negative object ids

Fix two errors introduced in #1110 and #1112. Since
#1110, encountering the invalid indirect reference #1110
-2147483648 n R produces an integer underflow which, if
 undetected, immediately trigger a logic error. Since
 #1112, object -1 0 R may be incorrectly identified as
 an earlier generation of itself and deleted,
 invalidating a live iterator.

Use std::vector instead of list and move shared pointers