Escape dbl quote and handle empty selecta result.

Hi,

There were two issues I noticed.

First issue:
1. Start a fresh copy of Vim and don't open any files.
2. ```:call SelectaFile()```
3. Hit *Escape* or any keystroke that cancels selecta without selecting a file.

The result is this error:

    Error detected while processing function SelectaFile..SelectaCommand:
    line   10:
    E32: No file name

Second issue:
1. Run a command that leaves a double quote character in command history, e.g. ```:echo '"'```
2. ```:call SelectaHistoryCommand()```

The result is this error, although it varies depending on what comes after the double quote character:

    Error detected while processing function SelectaHistoryCommand..SelectaFromList..SelectaCommand:
    line    2:
    E484: Can't open file /var/folders/mq/llkx61wn0zl1gr5jydzv8gq80000gn/T/vYV0fFg/5

This patch handles the empty selecta result from the first issue and escapes double quote characters to take care of the second issue.