MXKEventFormater: Fixed crash ("NSConcreteMutableAttributedString addAttribute:value:range:: nil value") when trying to display bad formated links ( like http://localhost:9000' ) and when "opening links in Chrome" is enabled.
MXKEventFormater: Fixed crash ("NSConcreteMutableAttributedString addAttribute:value:range:: nil value") when trying to display bad formated links ( like http://localhost:9000' ) and when "opening links in Chrome" is enabled.

Added sanity check to avoid this.

matrix-org/matrix-ios-kit,matrix-org/matrix-ios-kit,matrix-org/matrix-ios-kit,matrix-org/matrix-ios-kit