Only match completely blank entries.  Fixes #279.

The string didn't match over new line characters.

" \n "  => 0
"Test"  => nil
"a\n "  => 2
" \na"  => 0

This change has allows strings that start or end with white space
characters to display in the helm completion list.

" \n "  => 0
"Test"  => nil
"a\n "  => nil
" \na"  => nil