Improve handling of parsing multiple subfields

What does not work

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $atesting $btestingtwo
4. Expected outcome View MARC source shows and Edit quickMARC displays: $a testing $b testing two
5. Actual outcome: quickMARC does not save the MARC field/row.

What works

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $a testing $b testing two
4. Expected and Actual outcome > View MARC source shows and Edit quickMARC displays: $a testing $b testing two

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $atesting $b testing two
4. Expected and Actual outcome > View MARC source shows and Edit quickMARC displays: $a testing $b testing two

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $atesting $btesting two
4. Expected and Actual outcome > View MARC source shows and Edit quickMARC displays: $a testing $b testing two

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $a testing $btestingtwo
4. Expected and Actual outcome > View MARC source shows and Edit quickMARC displays: $a testing $b testing two

1. Edit a quickMARC record (any bib/holdings/authority)
2. Add a new MARC tag
3. Enter a subfield as followed: $atesting $b testingtwo
4. Expected and Actual outcome > View MARC source shows and Edit quickMARC displays: $a testing $b testing two