- Don't double-quote an already double-quoted argument.

dlls/shell32/shlexec.c

@@ -142,8 +142,10 @@ static BOOL SHELL_ArgifyW(WCHAR* out, int len, const WCHAR* fmt, const WCHAR* lp
                     else
                         cmd = lpFile;
 
-                    /* Add double quotation marks unless we already have them (e.g.: "file://%1" %* for exefile) */
-                    if (res == out || *(fmt + 1) != '"')
+                    /* Add double quotation marks unless we already have them
+                       (e.g.: "file://%1" %* for exefile) or unless the arg is already
+                       enclosed in double quotation marks */
+                    if ((res == out || *(fmt + 1) != '"') && *cmd != '"')
                     {
                         *res++ = '"';
                         strcpyW(res, cmd);
@@ -207,10 +209,14 @@ static BOOL SHELL_ArgifyW(WCHAR* out, int len, const WCHAR* fmt, const WCHAR* lp
                         strcpyW( res, tmpEnvBuff );
                     res += strlenW(res);
                 }
-                fmt++;
                 done = TRUE;
                 break;
             }
+            /* Don't skip past terminator (catch a single '%' at the end) */
+            if (*fmt != '\0')
+            {
+                fmt++;
+            }
         }
         else
             *res++ = *fmt++;