Fix some minor std::function-related bugs.

Lambdas to be stored in `function<void()>` should not return `bool`.

Two uses of `std::function` could be just `function`, like everywhere
else in the codebase.

dialogs.cpp

@@ -473,7 +473,7 @@ namespace dialog {
   
   color_t *colorPointer;
   
-  bool handleKeyColor(int sym, int uni) {
+  void handleKeyColor(int sym, int uni) {
     unsigned& color = *colorPointer;
     int shift = colorAlpha ? 0 : 8;
 
@@ -514,7 +514,6 @@ namespace dialog {
     else if(doexiton(sym, uni)) {
       popScreen();
       }
-    return false;
     }
   
   bool colorAlpha;

graph.cpp

@@ -1870,9 +1870,9 @@ int taildist(cell *c) {
   }
 
 int last_wormsegment = -1;
-vector<vector< std::function<void()> > > wormsegments;
+vector<vector< function<void()> > > wormsegments;
 
-void add_segment(int d, const std::function<void()>& s) {
+void add_segment(int d, const function<void()>& s) {
   if(isize(wormsegments) <= d) wormsegments.resize(d+1);
   last_wormsegment = max(last_wormsegment, d);
   wormsegments[d].push_back(s);
@@ -5778,7 +5778,7 @@ void drawscreen() {
   mouseovers = " ";
 
   cmode = 0;
-  keyhandler = [] (int sym, int uni) { return false; };
+  keyhandler = [] (int sym, int uni) {};
   #if CAP_SDL
   joyhandler = [] (SDL_Event& ev) { return false; };
   #endif

rogueviz-banachtarski.cpp

@@ -442,7 +442,7 @@ void bantar_anim() {
 
 bool bmap;
 
-bool bantar_stats() {
+void bantar_stats() {
   if(bmap) {
     vid.linewidth *= (inHighQual ? 10 : 2);
     for(auto p: parent) if(gmatrix.count(p.first) && gmatrix.count(p.second))
@@ -458,7 +458,6 @@ bool bantar_stats() {
     vid.linewidth /= (inHighQual ? 10 : 2);
     drawqueue();
     }
-  return false;
   }
 
 void init_bantar() {

rogueviz-graph.cpp

@@ -389,7 +389,7 @@ void show_graph() {
     };
   }
 
-bool frame() { 
+void frame() { 
   if(graphcolor) {
     hyperpoint h0 = find_point(0);
     hyperpoint h1 = find_point(1);
@@ -397,7 +397,6 @@ bool frame() {
     draw_to(0, h0, 1, h1);
     finish();
     }
-  return false;
   }
 
 #if CAP_COMMANDLINE