Don't end converting prematurely on encountering consecutive NULs.

Don't stop converting subsequent chunks just because the length of one of them
was 0: this can happen if the first character of a string is a NUL or if there
are two (or more) NULs in it later.

Simply remove the check for this and continue as usual even in this case.

Also add a unit test verifying that we do translate NULs in input into NULs in
output.

Closes #16620.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78021 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/strconv.cpp

@@ -232,12 +232,6 @@ wxMBConv::ToWChar(wchar_t *dst, size_t dstLen,
         if ( !srcEnd )
             dstWritten++;
 
-        if ( !lenChunk )
-        {
-            // nothing left in the input string, conversion succeeded
-            break;
-        }
-
         if ( dst )
         {
             if ( dstWritten > dstLen )

tests/strings/unicode.cpp

@@ -291,6 +291,10 @@ void UnicodeTestCase::ConversionWithNULs()
 
     CPPUNIT_ASSERT( memcmp(theLocalBuffer.data(), L"The\0String", 11 * sizeof(wchar_t)) == 0 );
 #endif // wxUSE_UNICODE/!wxUSE_UNICODE
+
+    const char *null4buff = "\0\0\0\0";
+    wxString null4str(null4buff, 4);
+    CPPUNIT_ASSERT_EQUAL( 4, null4str.length() );
 }
 
 void UnicodeTestCase::ConversionUTF7()