Styleistic changes

In reading of the code for File::Fetch, I found the standard way of isolating the body code for each fetcher a bit strange:

```perl

sub foo { 

   if ( $starting_condition ) { 
        # main code of the fetcher 
   } else {
        $METHOD_FAIL->{foo} = 1; 
        return;
   }
}
```
And this proves to be cognitive overhead that's not necessary , and makes most the code have a surplus indentation level it could do without, so this patch ( done in 2 parts, first part the block reordering, second part tidying indentation ) aims to solve that.

```perl

sub foo {

   unless ( $starting_condition ) { 
       $METHOD_FAIL->{foo} = 1;
       return;
   }
   # main code of the fetcher

}
```

In the process, I incidentally discovered the sort of problems I tend to expect from this slightly inefficient code style, a bug nobody seems to have reported yet and would be hard to notice, but if `_fetch_fetch()` fails, it will currently mark its failure by

```perl
$METHOD_FAIL->{wget} = 1
```