file: Support unicode urls on windows

Closes https://github.com/curl/curl/pull/6501

tests/data/Makefile.inc

@@ -201,7 +201,7 @@ test1630 test1631 test1632 test1633 test1634 \
 test1650 test1651 test1652 test1653 test1654 test1655 \
 test1660 \
 \
-test1700 test1701 test1702 \
+test1700 test1701 test1702 test1703 \
 \
 test1800 test1801 \
 \

tests/data/test1703

@@ -0,0 +1,45 @@
+<testcase>
+<info>
+<keywords>
+FILE
+</keywords>
+</info>
+
+<reply>
+<data>
+foo
+   bar
+bar
+   foo
+moo
+</data>
+</reply>
+
+# Client-side
+<client>
+<server>
+file
+</server>
+<features>
+Unicode
+win32
+</features>
+<name>
+basic file:// file with UTF-8 characters
+</name>
+<command option="no-include">
+file://localhost%FILE_PWD/log/%E3%83%86%E3%82%B9%E3%83%881703.txt
+</command>
+<file name="log/テスト1703.txt">
+foo
+   bar
+bar
+   foo
+moo
+</file>
+</client>
+
+# Verify data after the test has been "shot"
+<verify>
+</verify>
+</testcase>