The impact of falling oil prices in Alaska, which has seemed for many residents like a distant worry until now, is about to land. The turning point came on Friday, when the State House of Representatives, meeting at the Capitol in Juneau in the fifth special session since last summer, failed to override a line-item veto of the budget by Gov. Bill Walker. That means the $1.3 billion in spending cuts imposed last month by Mr. Walker, a political independent, will almost certainly take effect on top of cuts that lawmakers in the Republican-controlled Legislature had already agreed on.