Maruti Suzuki India — Front glass has been cracked automatically

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712233

I have bought a dzire car on June 2015, Till then it was fine but yesterday when I open the garage I saw one "L" type straight line crack is found on the front glass then I go to my Bhandari automobile workshop at serampore, hooghly and they told it's a air crack and they asked 4700. Now my question is what is the meaning of warranty. One parts of Your car has been broken automatically then why should I pay for this. Please resolve