only return one value for A if not astigmatic

src/new/zernike_polynomials/FT_Rc_to_Znm.m

@@ -52,8 +52,10 @@ function [A] = FT_Rc_to_Znm(Rc,R)
     % Calculate Z20 amplitude
     A(1) = (Ax+Ay)/2;
     
+    if length(Rc)>1
         % Calculate Z22 astigmatic amplitude
         A(2) = 2*(Ax-A(1));
+    end
 
     % Convert amplitudes to nm
     A = 1e9*A;