Do not attempt to split raw numeric GPS coordinates

Fixes exiftool-rb#7
If `-n` option is used, GPS coordinates come as numeric values and there is no need to attempt to split cardinal directions from the value.

Also added a test for this scenario.

Author: Sergey Morozov

lib/exiftool/field_parser.rb

@@ -46,6 +46,7 @@ def lat_long?
     end
 
     def as_lat_long
+      return raw_value if raw_value.is_a? Numeric
       value, direction = raw_value.split(' ')
       if value =~ /\A\d+\.?\d*\z/
         value.to_f * (['S', 'W'].include?(direction) ? -1 : 1)

test/field_parser_test.rb

@@ -85,4 +85,9 @@
     p = Exiftool::FieldParser.new('GPSLongitude', '122.47566667 W')
     p.value.must_be_close_to(-122.47566667)
   end
+
+  it 'parses numerical only GPS coordinates' do
+    p = Exiftool::FieldParser.new('GPSLongitude', -122.475666666667)
+    p.value.must_be_close_to(-122.475666666667)
+  end
 end