Close expr_array is_typecheck_error early return leak (#5217)

When is_typecheck_error(c_type) fires after the accumulator loop has run
at least one iteration, `type` may be a freshly-allocated orphan tree
from a prior type_union call. The adjacent AST_FLAG_JUMPS_AWAY exit
correctly calls ast_free_unattached(type) before returning, but this
path did not.

Closes #5212

Author: SeanTAllen

src/libponyc/expr/array.c

@@ -476,7 +476,10 @@ bool expr_array(pass_opt_t* opt, ast_t** astp)
 
     ast_t* c_type = ast_type(ele);
     if(is_typecheck_error(c_type))
+    {
+      ast_free_unattached(type);
       return false;
+    }
 
     if(told_type)
     {