Fix appendLengthEncodedInteger for large numbers > 0xffffff

[cxmcc]

If the value is ≥ (2^24) and < (2^64) it is stored as fe + 8-byte integer.

The current function seems to be ignoring this case xD.

[arnehormann]

LGTM

[cxmcc]

There was a typo actually, I just amended it. Suddenly realized 7*8 != 54...

[arnehormann]

Damn, I didn't catch that...
Please add a test (using an SQL statment).

[arnehormann]

And thanks again, good catch!

[cxmcc]

@arnehormann
These two issues affect only:
Number of affected rows > 0xffffff
String length > 0xffffff (actually found this bug when trying length = 2^25)

Which is pretty big..It will be quite hard to test with SQL statements for these rare cases. We should probably do some unit tests for these single functions?

[arnehormann]

Yes, you are right.
I'd like a roundtrip test with both functions in utils_test.go with the edge values of each possible range, then.

[julienschmidt]

Not roundtrip tests again 😄
+1 for unit tests

[arnehormann]

Roundtrip in this case: appendLengthEncodedInteger -> readLengthEncodedInteger, retrieve the exact same value that was entered. Not a database roundtrip.

[cxmcc]

@julienschmidt @arnehormann tests added.

[julienschmidt]

LGTM