''No Man's Land'' was shown as part of the 1985 New York Film Festival. Following are excerpts from Vincent Canby's review, which appeared in The New York Times Oct. 5, 1985. The film opens today at the Public Theater, 425 Lafayette Street. EACH of the four principal characters in Alain Tanner's ''No Man's Land'' wants to be someplace else. Madeleine, who runs a disco on the French-Swiss border, dreams of going to Paris to pursue a singing career. Her lover, Paul, who makes his living smuggling money, gold and goods across the border, plans to emigrate to Canada. Mali, a pretty young Algerian woman who lives in France and works in Switzerland, would like to be anywhere except where she is. Louis, born on a Swiss farm and trained as a clockmaker, would give anything to leave his mistress, Lucie, and move in with Mali.