lib: tutf8e: Resolve compiler warnings on Windows (#2884)
lib: tutf8e: Resolve compiler warnings on Windows (#2884)

This is a minor patch that resolves the following two warnings
on Microsoft Visual C++.

 * warning C4242: '=': conversion from 'const uint16_t'
   to 'unsigned char', possible loss of data

 * warning C4706: assignment within conditional expression

With this applied, tutf8e is warning-free on Windows.

Signed-off-by: Fujimoto Seiji <ef879192bb1e41d519c82cf76440dc8e9a530806@ceptord.net>
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