simplify the logic of save binary

Add checks for valid values
Fix wording on some errors

Declare vars as locally as possible

Initialize local variables

Remove unused var "total"
Declare vars as locally as possible

class LevMarqSparse is not tagged CV_EXPORTS, 
so the contrib module,  built the on win using vs won't contain that symbol,
trying to create an instance of LevMarqSparse will lead to a 'undefined symbol' err, because it did not make it into the library. 

Issue #2114

This follows SURF changes in 1f261c2f

Also corrected some indexes to be size_t.