Fix converting to Gregorian

[Korota-21]

it gives wrong date so I fix it

[khanzi05]

Hi @Korota-21 , Thanks for the PR, I have seen the similar issue.

For example, this code doesnot convert all the Hijri dates to Gregorian dates correct like

12-07-1408 Hijri is 29-02-1988 but this gives 29-02-1987 where there is no 29 Feb in 1987.

DO you think, this fix will work correctly ?

[Korota-21]

I have tried your example, and it works fine