refactor: SCHWED-4345 use same logic for IsValid and CheckValidity

In both cases we check if we have a valid implementation AND if the
underlying entity is still there.

modules/mol/base/src/atom_base.cc

@@ -104,12 +104,12 @@ String AtomBase::GetQualifiedName() const
 
 bool AtomBase::IsValid() const
 {
-  return Impl().get()!=0;
+  return Impl().get()!=0 && impl_->GetEntity();
 }
 
 void AtomBase::CheckValidity() const 
 {
-  if (! (impl_ && impl_->GetEntity()))
+  if (! IsValid())
     throw InvalidHandle();
 }
 

modules/mol/base/src/chain_base.cc

@@ -54,11 +54,11 @@ String ChainBase::GetDescription() const {
 
 bool ChainBase::IsValid() const
 {
-  return Impl().get()!=0;
+  return Impl().get()!=0 && impl_->GetEntity();
 }
 
 void ChainBase::CheckValidity() const {
-  if (! (impl_ && impl_->GetEntity()))
+  if (! IsValid())
     throw InvalidHandle();
 }
 

modules/mol/base/src/residue_base.cc

@@ -158,12 +158,12 @@ const impl::ResidueImplPtr& ResidueBase::Impl() const
 
 bool ResidueBase::IsValid() const
 {
-  return Impl().get()!=0;
+  return Impl().get()!=0 && impl_->GetEntity();
 }
 
 void ResidueBase::CheckValidity() const 
 {
-  if (! (impl_ && impl_->GetEntity()))
+  if (! IsValid())
     throw InvalidHandle();
 }