Problem parsing some GSE matrices

[grimbough]

The refactored code for parsing GSE matrices seems to fail in some cases e.g. GSE5350 which we use in the BeadArrayUseCases vignette.

A straightforward path to producing the error is to try calling parseGSEMatrix on the GEO series text file directly:

GEOquery:::parseGSEMatrix(fname = "ftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE5nnn/GSE5350/matrix/GSE5350-GPL2507_series_matrix.txt.gz")`

Error in enc2utf8(col_names(col_labels, sep = sep)) : 
  argument is not a character vector`

Some rudimentry digging leads me to think this is an issue with how the Sample_characteristics_ch1 field is being processed, but I don't know enough about how that may look across multiple datasets to offer a generic solution.

Happy to do some more experimentation if needed.

[grimbough]

After a bit more digging to find some example data where this was working as expected I've suggested a patch in #46