CHG: better handling of file vs version number

Author: MathieuMorlighem

src/m/modeldata/interpBedmachineAntarctica.m

@@ -31,7 +31,7 @@
 end
 basename = 'BedMachineAntarctica';
 
-if nargin==5
+if nargin==5 && exist(ncdate, 'file')
 	ncfile = ncdate;
 else
 	%List of common paths to try