[Bwa] Crash output to read-only folder

Regression, UCR-2094, minor issue.

1. Tools->NGS data analysis->Map reads to reference...
   The "Map NGS Reads to Reference" dialog appears.
2. Set:
   1. Mapping tool: BWA
   2. Reference sequence: _common_data/bwa/NC_000021.gbk.fa
   3. Result file name: someFolder/NC_000021.sam
   4. Short reads:
      1. _common_data/bwa/control-chr21.fastq
      2. _common_data/bwa/nrsf-chr21.fastq
3. Make "someFolder" read-only.
4. Click Start.
   Expected: the task ended with an error that the files couldn't be opened for writing.
   Current state: crash.