TW-1658: rc override to non-existent alternate rc quietly uses default

- Thanks to David Patrick.
- The 'rc:' argument now means 'use all defaults', which assumes
  'data.location=~/.task', so this will not work for anyone using a different
  location.

ChangeLog

@@ -15,6 +15,8 @@
           blank results (thanks to Jeremy John Reeder).
 - TW-1582 Wrong urgency for first report after reviving task with
           "mod status:pending"
+- TW-1658 rc override to non-existent alternate rc quietly uses default (thanks
+          to David Patrick).
 - TW-1698 tests: 'make test' should exit non-zero if tests failed
           (thanks to Daniel Shahaf).
 - TW-1703 When on-modify hook is installed, some messages print UUIDs

src/CLI2.cpp

@@ -254,7 +254,7 @@ void CLI2::getOverride (int argc, const char** argv, std::string& home, File& rc
     if (raw == "--")
       return;
 
-    if (raw.length () > 3 &&
+    if (raw.length () >= 3 &&
         raw.substr (0, 3) == "rc:")
     {
       rc = raw.substr (3);

src/Context.cpp

@@ -683,7 +683,7 @@ void Context::staticInitialization ()
 void Context::createDefaultConfig ()
 {
   // Do we need to create a default rc?
-  if (! rc_file.exists ())
+  if (rc_file._data != "" && ! rc_file.exists ())
   {
     if (config.getBoolean ("confirmation") &&
         !confirm (format (STRING_CONTEXT_CREATE_RC, home_dir, rc_file._data)))