mshtml: Make empty string is a valid overflow style.

dlls/mshtml/htmlstyle.c

@@ -2016,7 +2016,7 @@ static HRESULT WINAPI HTMLStyle_put_overflow(IHTMLStyle *iface, BSTR v)
     TRACE("(%p)->(%s)\n", This, debugstr_w(v));
 
     /* overflow can only be one of the follow values. */
-    if(!v || strcmpiW(szVisible, v) == 0 || strcmpiW(szScroll, v) == 0 ||
+    if(!v || !*v || strcmpiW(szVisible, v) == 0 || strcmpiW(szScroll, v) == 0 ||
              strcmpiW(szHidden, v) == 0  || strcmpiW(szAuto, v) == 0)
     {
         return set_nsstyle_attr(This->nsstyle, STYLEID_OVERFLOW, v, 0);

dlls/mshtml/tests/dom.c

@@ -3441,6 +3441,16 @@ static void test_default_style(IHTMLStyle *style)
     ok(!strcmp_wa(str, "auto"), "str=%s\n", wine_dbgstr_w(str));
     SysFreeString(str);
 
+    str = a2bstr("");
+    hres = IHTMLStyle_put_overflow(style, str);
+    ok(hres == S_OK, "put_overflow failed: %08x\n", hres);
+    SysFreeString(str);
+
+    hres = IHTMLStyle_get_overflow(style, &str);
+    ok(hres == S_OK, "get_overflow failed: %08x\n", hres);
+    ok(!str, "str=%s\n", wine_dbgstr_w(str));
+    SysFreeString(str);
+
     /* restore overflow default */
     hres = IHTMLStyle_put_overflow(style, sOverflowDefault);
     ok(hres == S_OK, "put_overflow failed: %08x\n", hres);