duphandle: also init netrc

The netrc init was only done in the Curl_open, meaning that a duplicated
handle would not get inited properly.

Added test 2309 to verify. It does netrc auth with a duplicated handle.

Regression from 3b43a05e00

Reported-by: tranzystorekk on github
Fixes #15496
Closes #15503

tests/data/Makefile.am

@@ -255,7 +255,7 @@ test2100 \
 test2200 test2201 test2202 test2203 test2204 test2205 \
 \
 test2300 test2301 test2302 test2303 test2304 test2305 test2306 test2307 \
-test2308 \
+test2308 test2309 \
 \
 test2400 test2401 test2402 test2403 test2404 test2405 test2406 \
 \

tests/data/test2309

@@ -0,0 +1,66 @@
+<testcase>
+<info>
+<keywords>
+netrc
+HTTP
+</keywords>
+</info>
+#
+# Server-side
+<reply>
+<data crlf="yes" nocheck="yes">
+HTTP/1.1 200 OK
+Date: Tue, 09 Nov 2010 14:49:00 GMT
+Server: test-server/fake
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT
+ETag: "21025-dc7-39462498"
+Accept-Ranges: bytes
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+<features>
+proxy
+</features>
+
+# Reproducing issue 15496
+<name>
+HTTP with .netrc using duped easy handle
+</name>
+<tool>
+lib%TESTNUMBER
+</tool>
+<command>
+http://github.com %LOGDIR/netrc%TESTNUMBER http://%HOSTIP:%HTTPPORT/
+</command>
+<file name="%LOGDIR/netrc%TESTNUMBER" >
+
+machine github.com
+
+login daniel
+password $y$j9T$WUVjiVvDbRAWafDLs6cab1$01NX.oaZKf5lw8MR2Nk9Yaxv4CqbE0IaDF.GpGxPul1
+</file>
+</client>
+
+<verify>
+<protocol>
+GET http://github.com/ HTTP/1.1
+Host: github.com
+Authorization: Basic %b64[daniel:$y$j9T$WUVjiVvDbRAWafDLs6cab1$01NX.oaZKf5lw8MR2Nk9Yaxv4CqbE0IaDF.GpGxPul1]b64%
+Accept: */*
+Proxy-Connection: Keep-Alive
+
+</protocol>
+</verify>
+</testcase>