get_ssm_by_sample returns non informative error when using non-existent sample ID.

[mattssca]

By mistake, I discovered this error. This is also a reminder that there are outstanding functions in GAMBLR.results that should make use of id_ease in dealing with sample IDs (similar to how the corresponding functions in GAMBLR.data works). By having the function call the helper (id_ease) this error would be much easier to understand.

> this_sample_df = get_ssm_by_sample(this_sample_id = "DOOHH-2",
+                                     this_seq_type = "genome")
Error in if (pair_status == "unmatched") { : argument is of length zero