My linea's front windscreen cracked. Windscreen was ok in morning. I was pretty sure of it since i myself cleaned it before i drove. After reaching my office parking lot( open parking lot under the sun), there was a linear crack on windscreen at lower left corner when i came back in afternoon time. The crack was extended from bottom of the windscreen to about 1/3rd of its height. Edged was not felt when finger was rubbed against the crack. There was not a visible evidence of impact. What could be its cause? what do you suggest as possible solution?