Do not allow repeating last insert when we are not in normal mode

<a-;>. is not accepted anymore. Note that <a-;> are not repeatable
currently anyway (That could be fixed, athough not trivial).
Fixes #1469

src/input_handler.cc

@@ -1430,6 +1430,9 @@ void InputHandler::repeat_last_insert()
     if (m_last_insert.keys.empty())
         return;
 
+    if (dynamic_cast<InputModes::Normal*>(&current_mode()) == nullptr)
+        throw runtime_error{"repeating last insert not available in this context"};
+
     Vector<Key> keys;
     swap(keys, m_last_insert.keys);
     ScopedSetBool disable_hooks(context().hooks_disabled(),

test/regression/1469-assert-on-repeat-insert/cmd

@@ -0,0 +1 @@
+i<a-;>!echo tchou<ret><a-;>.

test/regression/1469-assert-on-repeat-insert/in

@@ -0,0 +1 @@
+

test/regression/1469-assert-on-repeat-insert/out

@@ -0,0 +1,2 @@
+tchou
+

test/regression/787-crash-after-S/out

@@ -0,0 +1 @@
+

test/run

@@ -19,7 +19,7 @@ main() {
             eval -buffer *debug* write debug
             quit!
         }
-        exec "%sh{cat cmd}"
+        try %{ exec "%sh{cat cmd}" }
         exec <c-l>
         eval -buffer *debug* write debug
         nop %sh{