wkb/encoding package: check if Byte Order Marker is correctly set before processing stream

[chebizarro]

One of the errors detected by fuzzing (#53, #384) was the creation of valid geometries from corrupt data. This patch goes some ways to remedying this by checking if the BOM is correctly set (0 or 1) as per the specification and returning an error if it is any other value.

[coveralls]

Pull Request Test Coverage Report for Build 979

• 0 of 0 (NaN%) changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 46.31%

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Files with Coverage Reduction	New Missed Lines	%
provider/gpkg/binary_header.go	2	100.0%

Totals
Change from base Build 977:	0.0%
Covered Lines:	5824
Relevant Lines:	12576

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💛 - Coveralls

[gdey]

LGTM