Always catch exception when variable not present in file

This probably either means an old output file, or some variable that is
not always written out (e.g. the PI controller integral terms). Neither
of these is a bug/issue that needs fixing, so makes sense to catch the
error and continue even if `handle_errors = false` is set in the
post-processing input file.

makie_post_processing/makie_post_processing/src/plots_for_variable.jl

@@ -53,9 +53,15 @@ function plots_for_variable(run_info, variable_name; plot_prefix, has_rdim=true,
     try
         variable = get_variable(run_info, variable_name)
     catch e
-        return makie_post_processing_error_handler(
-                   e,
-                   "plots_for_variable() failed for $variable_name - could not load data.")
+        if isa(e, KeyError)
+            println("Key $(e.key) not found when loading $variable_name - probably not "
+                    * "present in output")
+            return nothing
+        else
+            return makie_post_processing_error_handler(
+                       e,
+                       "plots_for_variable() failed for $variable_name - could not load data.")
+        end
     end
 
     if variable_name ∈ em_variables