Fix add_genome_matches

DESCRIPTION

 Package: multicrispr
 Title: Multi-locus multi-purpose Crispr/Cas design 
-Version: 0.99.33
+Version: 0.99.34
 Encoding: UTF-8
 Authors@R: c(person("Aditya",   "Bhagwat",    NULL, "aditya.bhagwat@mpi-bn.mpg.de",   c("aut", "cre")),
             person( "Johannes", "Graumann",   NULL, 'johannes.graumann@mpi-bn.mpg.de',c("sad", "ctb")),

R/07_count_offtargets.R

@@ -594,6 +594,7 @@ add_genome_matches <- function(
     verbose           = TRUE
 ){
     assert_is_subset(offtargetmethod, c('bowtie', 'pdict'))
+    if (!has_been_indexed(bsgenome, indexedgenomesdir)) return(spacers)
     if (offtargetmethod=='bowtie'){
         add_genome_matches_bowtie(
             spacers  = spacers, bsgenome = bsgenome, mismatches = mismatches,