ENH: failsafe version of Istream peek()

- return undefinedToken on error

STYLE: fix slicing of ITstream from dictionary lookup

src/OpenFOAM/primitives/functions/Function1/Constant/Constant.C

@@ -52,7 +52,7 @@ Foam::Function1Types::Constant<Type>::Constant
     Function1<Type>(entryName, dict),
     value_(Zero)
 {
-    Istream& is = dict.lookup(entryName);
+    ITstream& is = dict.lookup(entryName);
     word entryType(is);
     is  >> value_;
 }

src/OpenFOAM/primitives/functions/Function1/Function1/Function1New.C

@@ -65,7 +65,7 @@ Foam::Function1<Type>::New
         // - non-word : value for constant function
         // - word : the modelType
 
-        Istream& is = eptr->stream();
+        ITstream& is = eptr->stream();
 
         token firstToken(is);
 

src/OpenFOAM/primitives/functions/Function1/PolynomialEntry/PolynomialEntry.C

@@ -41,7 +41,7 @@ Foam::Function1Types::Polynomial<Type>::Polynomial
     coeffs_(),
     canIntegrate_(true)
 {
-    Istream& is = dict.lookup(entryName);
+    ITstream& is = dict.lookup(entryName);
     const word entryType(is);
 
     is  >> coeffs_;

src/OpenFOAM/primitives/functions/Function1/Table/Table.C

@@ -39,7 +39,7 @@ Foam::Function1Types::Table<Type>::Table
 :
     TableBase<Type>(entryName, dict)
 {
-    Istream& is = dict.lookup(entryName);
+    ITstream& is = dict.lookup(entryName);
     const word entryType(is);
     is  >> this->table_;
     TableBase<Type>::check();