Fix some I/O returns

BGL/include/CGAL/boost/graph/IO/GOCAD.h

@@ -107,7 +107,7 @@ public:
       std::getline(input, s);
     }
 
-    return true;
+    return !input.fail();
   }
 };
 
@@ -143,7 +143,7 @@ bool read_GOCAD(std::istream& in,
   name = builder.name;
   color = builder.color;
 
-  return g.is_valid(); // @fixme keep validity check?
+  return is_valid(g); // @fixme keep validity check?
 }
 
 /*!

Stream_support/include/CGAL/IO/OBJ.h

@@ -87,7 +87,7 @@ bool read_OBJ(std::istream& input,
     return false;
   }
 
-  return true;
+  return !input.fail();
 }
 
 } // namespace CGAL

Stream_support/include/CGAL/IO/OFF.h

@@ -67,7 +67,7 @@ bool read_OFF(std::istream& in,
       scanner.skip_to_next_vertex(i);
     }
 
-    if(!in)
+    if(!in.good())
       return false;
   }
 
@@ -77,7 +77,7 @@ bool read_OFF(std::istream& in,
     std::size_t no;
     scanner.scan_facet(no, i);
 
-    if(!in)
+    if(!in.good())
       return false;
 
     IO::internal::resize(polygons[i], no);
@@ -114,7 +114,7 @@ bool read_OFF(std::istream& in,
     }
   }
 
-  return in.good();
+  return !in.fail();
 }
 
 /*!
@@ -163,7 +163,7 @@ bool read_OFF(std::istream& in,
     }
   }
 
-  return in.good();
+  return !in.fail();
 }
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////

Stream_support/include/CGAL/IO/STL/STL_reader.h

@@ -121,7 +121,7 @@ bool parse_ASCII_STL(std::istream& input,
     std::cout << "Parsing ASCII file..." << std::endl;
 
   if(!input.good())
-    return true;
+    return false;
 
   // Here, we have already read the word 'solid'
 
@@ -158,7 +158,7 @@ bool parse_ASCII_STL(std::istream& input,
     return false;
   }
 
-  return true;
+  return !input.fail();
 }
 
 template <class PointRange, class TriangleRange>
@@ -178,7 +178,7 @@ bool parse_binary_STL(std::istream& input,
   input.seekg(0, std::ios::beg);
 
   if(!input.good())
-    return true;
+    return false;
 
   // Discard the first 80 chars (unused header)
   int pos = 0;
@@ -281,7 +281,7 @@ bool parse_binary_STL(std::istream& input,
     }
   }
 
-  return true;
+  return !input.fail();
 }
 
 } // namespace internal