[pretty] fix crash when rewriting lines

src/default-log-formats.json

@@ -1282,7 +1282,8 @@
         "value" : {
             "syscall" : {
                 "kind" : "string",
-                "identifier" : true
+                "identifier" : true,
+                "rewriter" : ":pipe-line-to explain-syscall.sh ${syscall}"
             },
             "args" : {
                 "kind" : "string"

src/textview_curses.hh

@@ -650,7 +650,9 @@ public:
 
     textview_curses &set_sub_source(text_sub_source *src) {
         this->tc_sub_source = src;
-        src->register_view(this);
+        if (src) {
+            src->register_view(this);
+        }
         this->reload_data();
         return *this;
     };

src/view_helpers.cc

@@ -73,6 +73,7 @@ static void open_pretty_view(void)
     attr_line_t full_text;
 
     delete pretty_tc->get_sub_source();
+    pretty_tc->set_sub_source(nullptr);
     if (top_tc->get_inner_height() == 0) {
         pretty_tc->set_sub_source(new plain_text_source(NOTHING_MSG));
         return;

test/test_json_format.sh

@@ -36,8 +36,10 @@ check_output "json log format is not working" <<EOF
 EOF
 
 
-run_test ${lnav_test} -n \
-    -I ${test_dir} -c ':switch-to-view pretty' \
+run_test ${lnav_test} -n -I ${test_dir} \
+    -c ':switch-to-view pretty' \
+    -c ':switch-to-view log' \
+    -c ':switch-to-view pretty' \
     ${test_dir}/logfile_json.json
 
 check_output "json log format is not working" <<EOF