epicsStrnEscapedFromRaw may print inclomplete escape sequences

When epicsStrnEscapedFromRaw runs out of buffer space in the middle of an escape sequence, it prints incomplete and thus invalid sequences.
For example printing "\xff" (1 byte 0xff) into a buffer that is too short may result in `\`, `\x`, or `\xf`. In particular a stray `\` at the end may be misinterpreted for example when the escaped string itself is printed in quotes and then the outer ending quote gets "escaped".

Instead of printing incomplete sequences it should rather not print the sequence at all.