STYLE: simplify short-circuit involving autoPtr (#1775)

- with '&&' conditions, often better to check for non-null autoPtr
  first (it is cheap)

- check as bool instead of valid() method for cleaner code, especially
  when the wrapped item itself has a valid/empty or good.
  Also when handling multiple checks.

  Now
      if (ptr && ptr->valid())
      if (ptr1 || ptr2)

  instead
      if (ptr.valid() && ptr->valid())
      if (ptr1.valid() || ptr2.valid())

src/functionObjects/field/reactionSensitivityAnalysis/reactionsSensitivityAnalysis.C

@@ -34,7 +34,7 @@ template<class chemistryType>
 void Foam::functionObjects::reactionsSensitivityAnalysis<chemistryType>::
 createFileNames()
 {
-    if (writeToFile() && !prodFilePtr_.valid())
+    if (writeToFile() && !prodFilePtr_)
     {
         prodFilePtr_ = createFile("production");
         writeHeader(prodFilePtr_(), "production");