Ensure that exact_model is set before zero_key is called

zero_key(key) sets key%exact equal to the value of exact_model
In the previous code, zero_key was called before exact_model was set,
and so key%exact was set based on node_value("exact ") of the previous node.
So, move the code to set exact_model to before zero_key is called.

src/madx_ptc_module.f90

@@ -564,6 +564,14 @@ subroutine ptc_input()
 
     ord_max = -1
 
+    exact1=node_value("exact ")
+
+    if(exact1.eq.0.or.exact1.eq.1) then
+       EXACT_MODEL = exact1 .ne. 0
+    else
+       EXACT_MODEL = exact0
+    endif
+
     call zero_key(key)
 
     !j=j+1
@@ -617,14 +625,6 @@ subroutine ptc_input()
        metd = method0
     endif
 
-    exact1=node_value("exact ")
-
-    if(exact1.eq.0.or.exact1.eq.1) then
-       EXACT_MODEL = exact1 .ne. 0
-    else
-       EXACT_MODEL = exact0
-    endif
-
     !special node keys
     key%list%permfringe=node_value("fringe ") ! transfer(node_value("fringe ") .ne. zero, key%list%permfringe)
     key%list%bend_fringe=node_value("bend_fringe ") .ne. zero