[apps/graph/values] Fix k_maxNumberOfDisplayableSymbolTypes

Fix fuzzer crash:
1. Go to graph
2. Create 1 function of x, 1 of t and 1 of theta
3. Go to values
4. Move 3 times Right and then 2 times Left

Problem was that k_maxNumberOfDisplayableSymbolTypes was 2 but actually
it is 3.

apps/graph/values/values_controller.h

@@ -11,6 +11,7 @@
 #include <escher/even_odd_editable_text_cell.h>
 #include <escher/even_odd_message_text_cell.h>
 #include <escher/toggleable_dot_view.h>
+#include <omg/round.h>
 
 #include "derivative_parameter_controller.h"
 #include "interval_parameter_selector_controller.h"
@@ -67,7 +68,8 @@ class ValuesController : public Shared::ValuesController,
  private:
   constexpr static size_t k_maxNumberOfSymbolTypes =
       Shared::ContinuousFunctionProperties::k_numberOfSymbolTypes;
-  constexpr static int k_maxNumberOfDisplayableSymbolTypes = 2;
+  constexpr static int k_maxNumberOfDisplayableSymbolTypes =
+      OMG::Ceil(static_cast<float>(k_maxNumberOfDisplayableColumns) / 2.0f);
   constexpr static int k_maxNumberOfDisplayableAbscissaCells =
       k_maxNumberOfDisplayableSymbolTypes * k_maxNumberOfDisplayableRows;
   constexpr static int k_valuesCellBufferSize =

omg/include/omg/round.h

@@ -11,6 +11,12 @@ static inline T LaxToZero(T x) {
                                                          : x;
 }
 
+// std::ceil is not constexpr
+constexpr int Ceil(float f) {
+  const int i = static_cast<int>(f);
+  return f > static_cast<float>(i) ? i + 1 : i;
+}
+
 }  // namespace OMG
 
 #endif