MSVC include arguments can be invalid on remote workers if they are empty

[Dandielo]

fastbuild/Code/Tools/FBuild/FBuildCore/Graph/ObjectNode.cpp

Line 1601 in fc2a08e

fullArgs += '\\';

Jobs with relative include arguments passed to a remote worker are updated to absolute using the GetRemoteSourceRoot() value, this opens the possibility to end up with an include like this '-I"D:\my_workspace\" which will result in the rest of the command line to be parsed by MSVC as a single include statement.

[ffulin]

I'd like to ensure I we create a test to cover this case along with the fix. Could you please detail the exact string being specified for the include path on the command line (.CompilerOptions)?

[Dandielo]

This happened with an include coming from a empty string variable.

.IncludePathInVariable = ''

ObjectList( '...' )
{
.CompilerOptions + ' -I"$IncludePathInVariable$"'
}