Assert failing in debug build for MSVC 2017 14.1

[Drazuam]

There's an issue with FFTextStream.cpp looking at memory before it's char buffer, which is throwing an exception on debug builds in windows. Looks like it probably wouldn't be much of an issue on a "dumber" build or system that's not checking these types of things.

Simple fix though. line 157:

GPSTk/core/lib/FileHandling/FFTextStream.cpp

Line 157 in 997d97d

while (*line.rbegin() == '\r')

needs to change to:
while (line[0]!='\0' && *line.rbegin() == '\r')

This will cause the while to exit before it can check the rbegin() function, and it wont access memory wrongly.

Edit: I made this change and it solved the issue for me locally