As per Fiqh Hanafi, there is no Salaat before the Fardh Salaat of Salaat Ul Maghrib. There is some Sunnah Salaat between the Adhaan and Iqamah of every Salaat, but there is no such Salaat between the Adhaan and Iqamah of Salaat Ul Maghrib. It is Mustahab (commendable) to stand for Fardh Salaat immediately after the Adhaan.
There is no Salaat before the Fardh of Salaat Ul Maghrib
There is a Hadith in Zujajatul Masabeeh:
Translation of Hadith: Hadhrat Hayyan Bin Abdullah (May Allah be well pleased with him) narrates on the authority of his father that the Holy Prophet (Sallallahu alaihi wa sallam) said: There is Salaat between the Adhaan and Iqamah of every Salaat, except for Salaat Ul Maghrib. (Zujajatul Masabeeh, Vol. 1, Pg. No. 335)
The Holy Prophet (Sallallahu alaihi wa sallam) did not offer any Salaat before Maghrib
The Holy Prophet (Sallallahu alaihi wa sallam) did not offer any Salaat between the Adhaan and Iqamah of Salaat Ul Maghrib, as given in Zujajatul Masabeeh on the authority of Kitabul Aathaar of Imam Muhammad (May Allah shower His mercy on him):
Translation: It has been narrated on the authority of Hadhrat Hammad (May Allah shower His mercy on him), that he said: I asked Hadhrat Ibrahim Nakha’i (May Allah be well pleased with him) about the Salaat before the Fardh of Maghrib, he forbade me from doing so and said that the Holy Prophet (Sallallahu alaihi wa sallam) and Hadhrat Abu Bakr and Hadhrat Umar (May Allah be well pleased with them) did not offer this Salaat. (Zujajatul Masabeeh, Vol. 1, Pg. No. 336)
The Sahabah too did not offered Salaat before Salaat Ul Maghrib
Other Sahabah also did not offer any Salaat before Salaat Ul Maghrib, as given in Zujajatul Masabeeh:
Translation of Hadith: It has been narrated on the authority of Hadhrat Taoos (May Allah be well pleased with him) that he said: Hadhrat Abdullah Bin Umar (May Allah be well pleased with them) was asked about the 2 Raka'at before (Fardh of) Maghrib and he said: I did not see anyone in the blessed time of the Holy Prophet (Sallallahu alaihi wa sallam) offering this Salaat. (Zujajatul Masabeeh, Vol. 1, Pg. No. 336)
Thus, it is Makruh (undesirable) to offer any Sunnah or Nafl Salaat before the Fardh of Salaat Ul Maghrib, as given in Haashiya Al Tahawi Ala Miraqil Falah, Pg. No. 470.