Fixed several warnings with fallthrough on gcc 8

src/OpenMesh/Apps/Decimating/decimater.cc

@@ -464,7 +464,7 @@ int main(int argc, char* argv[])
       {
         case 'D': opt.decorate_name = true;   break;
         case 'd': gdebug            = true;   break;
-        case 'h': usage_and_exit(0);
+        case 'h': usage_and_exit(0); break;
         case 'i': ifname            = optarg; break;
         case 'M': opt.parse_argument( optarg ); break;
         case 'n': opt.n_collapses   = float(atof(optarg)); break;

src/OpenMesh/Apps/Decimating/decimaterviewer.cc

@@ -98,6 +98,7 @@ int main(int argc, char **argv)
        case 's': opt += OpenMesh::IO::Options::Swap; break;
        case 'h':
           usage_and_exit(0);
+          break;
        default:
           usage_and_exit(1);
      }

src/OpenMesh/Apps/QtViewer/meshviewer.cc

@@ -95,6 +95,7 @@ int main(int argc, char **argv)
        case 'b': opt += OpenMesh::IO::Options::Binary; break;
        case 'h':
           usage_and_exit(0);
+          break;
        case 's': opt += OpenMesh::IO::Options::Swap; break;
        default:
           usage_and_exit(1);

src/OpenMesh/Apps/Smoothing/smooth.cc

@@ -136,7 +136,7 @@ int main(int argc, char **argv)
 	  : SmootherT<MyMesh>::Normal;
 	break;
 
-      case 'h': usage_and_exit(0);
+      case 'h': usage_and_exit(0); break;
       case '?':
       default:  usage_and_exit(1);
     }

src/OpenMesh/Apps/Subdivider/adaptive_subdivider.cc

@@ -170,7 +170,7 @@ int main(int argc, char **argv)
       case 'm': { std::stringstream s; s << optarg; s >> max_nv; } break;
       case 'r': rule_sequence = optarg; break;
       case 'U': uniform = true; break;
-      case 'h': usage_and_exit(argv[0],0);
+      case 'h': usage_and_exit(argv[0],0); break;
       case '?':
       default:  usage_and_exit(argv[0],1);
     }

src/OpenMesh/Apps/Subdivider/subdivider.cc

@@ -234,7 +234,7 @@ int main(int argc, char **argv)
         }
         break;
       }
-      case 'h': usage_and_exit(0);
+      case 'h': usage_and_exit(0); break;
       case '?':
       default:  usage_and_exit(1);
     }

src/OpenMesh/Apps/VDProgMesh/Analyzer/vdpmanalyzer.cc

@@ -276,7 +276,7 @@ int main(int argc, char **argv)
     {
       case 'v': verbose = true; break;
       case 'o': ofname = optarg;  break;
-      case 'h': usage_and_exit(0);
+      case 'h': usage_and_exit(0); break;
       default:  usage_and_exit(1);
     }
   }

src/OpenMesh/Apps/VDProgMesh/mkbalancedpm/mkbalancedpm.cc

@@ -259,6 +259,7 @@ int main(int argc, char **argv)
       case 'I': enable_modIS = true; break;
       case 'h':
         usage_and_exit(0);
+        break;
       default:
 	usage_and_exit(1);
     }

src/OpenMesh/Apps/mconvert/mconvert.cc

@@ -183,6 +183,7 @@ int main(int argc, char *argv[] )
       case 'o': ofname = optarg; break;
       case 'h':
         usage_and_exit(0);
+        break;
       case '?':
       default:
         usage_and_exit(1);