Make leading nulls a special case to avoid breaking decoding some short strings in fallback encoding

tests/mbconv/convautotest.cpp

@@ -47,6 +47,7 @@ private:
         CPPUNIT_TEST( UTF8NoBom );
         CPPUNIT_TEST( Fallback );
         CPPUNIT_TEST( FallbackMultibyte );
+        CPPUNIT_TEST( FallbackShort );
         CPPUNIT_TEST( StreamUTF8NoBOM );
         CPPUNIT_TEST( StreamUTF8 );
         CPPUNIT_TEST( StreamUTF16LE );
@@ -100,6 +101,7 @@ private:
     void UTF8NoBom();
     void Fallback();
     void FallbackMultibyte();
+    void FallbackShort();
 
     // test whether two lines of text are converted properly from a stream
     void TestTextStream(const char *src,
@@ -222,6 +224,13 @@ void ConvAutoTestCase::FallbackMultibyte()
 #endif
 }
 
+void ConvAutoTestCase::FallbackShort()
+{
+    TestFirstChar("\x61\x61\x61\xc4", 'a', 4,
+                  ConvState(wxBOM_None, wxFONTENCODING_ISO8859_5, true),
+                  wxFONTENCODING_ISO8859_5);
+}
+
 void ConvAutoTestCase::TestTextStream(const char *src,
                                       size_t srclength,
                                       const wxString& line1,