(Reuters) - Caterpillar Inc on Friday forecast worse-than-expected earnings for this year after reporting lower sales across all three primary segments in the last quarter, offering further evidence of strains in the U.S. industrial economy.The world's biggest construction and mining equipment maker said it expects 2020 profit of $8.50 to $10 per share, lower than $11.06 per share last year and below the average analyst estimate of $10.63 per share.The Deerfield, Illinois-based company,..