shlwapi: Handle buffer overflow on A->W converter.

dlls/shlwapi/path.c

@@ -2344,7 +2344,12 @@ BOOL WINAPI PathCanonicalizeA(LPSTR lpszBuf, LPCSTR lpszPath)
   {
     WCHAR szPath[MAX_PATH];
     WCHAR szBuff[MAX_PATH];
-    MultiByteToWideChar(CP_ACP,0,lpszPath,-1,szPath,MAX_PATH);
+    int ret = MultiByteToWideChar(CP_ACP,0,lpszPath,-1,szPath,MAX_PATH);
+
+    if (!ret) {
+	WARN("Failed to convert string to widechar (too long?), LE %d.\n", GetLastError());
+	return FALSE;
+    }
     bRet = PathCanonicalizeW(szBuff, szPath);
     WideCharToMultiByte(CP_ACP,0,szBuff,-1,lpszBuf,MAX_PATH,0,0);
   }

dlls/shlwapi/tests/path.c

@@ -908,9 +908,9 @@ static void test_PathCanonicalizeA(void)
     lstrcpy(dest, "test");
     SetLastError(0xdeadbeef);
     res = PathCanonicalizeA(dest, too_long);
+    ok(!res, "Expected failure\n");
     todo_wine
     {
-        ok(!res, "Expected failure\n");
         ok(GetLastError() == 0xdeadbeef, "Expected 0xdeadbeef, got %d\n", GetLastError());
     }
     ok(lstrlen(too_long) == LONG_LEN - 1, "Expected length LONG_LEN - 1, got %i\n", lstrlen(too_long));