netrc: treat failure to find home dir same as missing netrc file

This previously caused a fatal error (with a confusing error code, at
that).

Reported by: Glen A Johnson Jr.

RELEASE-NOTES

@@ -57,6 +57,7 @@ This release includes the following bugfixes:
  o gnutls: fixed compilation against versions < 2.12.0
  o build: Fixed overridden compiler PDB settings in VC7 to VC12
  o ntlm_wb: Fixed buffer size not being large enough for NTLMv2 sessions [11]
+ o netrc: don't abort if home dir cannot be found
 
 This release includes the following known bugs:
 

lib/netrc.c

@@ -88,7 +88,7 @@ int Curl_parsenetrc(const char *host,
     }
 
     if(!home)
-      return -1;
+      return retcode; /* no home directory found (or possibly out of memory) */
 
     netrcfile = curl_maprintf("%s%s%s", home, DIR_CHAR, NETRC);
     if(home_alloc)