Fix spurious incremental search when incsearch=false

Regressed in a2c41593a (Fix partial regex text being pushed in history,
2023-11-02).

src/normal.cc

@@ -860,7 +860,9 @@ void regex_prompt(Context& context, String prompt, char reg, T func)
                 {
                 case PromptEvent::Abort: return;
                 case PromptEvent::Change:
-                    if (incsearch and not str.empty())
+                    if (not incsearch)
+                        return;
+                    if (not str.empty())
                         RegisterManager::instance()[reg].set(context, str.str());
                     break;
                 case PromptEvent::Validate:

test/regression/0-no-incsearch/cmd

@@ -0,0 +1 @@
+

test/regression/0-no-incsearch/in

@@ -0,0 +1,3 @@
+
+x1
+x2

test/regression/0-no-incsearch/kak_selection

@@ -0,0 +1 @@
+x1

test/regression/0-no-incsearch/rc

@@ -0,0 +1 @@
+set-option global incsearch false

test/regression/0-no-incsearch/script

@@ -0,0 +1,6 @@
+ui_out -ignore 4
+ui_in '{ "jsonrpc": "2.0", "method": "keys", "params": [ "/x" ] }'
+sleep 0.1
+ui_in '{ "jsonrpc": "2.0", "method": "keys", "params": [ ".<ret>" ] }'
+sleep 0.1
+ui_out -ignore 1