Fixes for issues Coverity has reported (VPP-972)

Fixes for issues Coverity has reported (VPP-972)

177117: fstat() returns -1 on error; the code is
        checking for any positive value instead
175142: final return could never be reached; simple
        refactoring
175235,175236: Warning suppressed with an explicit
        cast to (void)
174817: Final return couldn't be reached; is
        is_in_order is 0 then 'rv' is already returned
        above
172095,172093: If is_is_set does not get set to 1,
        then return 0 has already been invoked
174405: Re-kill this (nothing sets rv)
171136: Looks like a cmd line flag to set test_bytes
        was missing; added it, and refactored the
        argc/argv processing to avoid two other
        potential segv's
176813: Add range checking for term width/height.
        First stab at a reasonable range is 1-512
        for both.
175350: Fix implicit casting in shift operation
174272: Not a c+p error; try using a coverity
        annotation to ignore it
174273,175320: Annotated FORWARD_NULL

Change-Id: I58d0f860fc2209f59f8d1b6b344d631b8d429ace
Signed-off-by: Chris Luke <chrisy@flirble.org>