Report 1-based positions in wxFileConfig warning message

0-based positions are probably not what the users expect.

src/common/fileconf.cpp

@@ -2151,7 +2151,7 @@ static wxString FilterInValue(const wxString& str)
             else if ( i != end - 1 )
             {
                 wxLogWarning(_("unexpected \" at position %zu in '%s'."),
-                             i - str.begin(), str);
+                             i - str.begin() + 1, str);
             }
             //else: it's the last quote of a quoted string, ok
         }

tests/config/fileconf.cpp

@@ -657,7 +657,7 @@ TEST_CASE_METHOD(LogTestCase, "wxFileConfig::Error", "[fileconfig][error]")
     checkWarning("foo=\\", "trailing backslash");
 
     // Check that it's the second quote which is unexpected, not the first one.
-    checkWarning(R"(foo="x"y)", R"(unexpected " at position 2)");
+    checkWarning(R"(foo="x"y)", R"(unexpected " at position 3)");
 }
 
 #endif // wxUSE_FILECONFIG