Add to Processor non-throwing methods to get plugins

Complement the existing methods to access plugins in the class Processor
with non-throwing versions. Instead of raising an exception they return
a null pointer in a state of error.

core/include/Processor.hpp

@@ -95,6 +95,14 @@ class Processor
          */
         Plugin const *GetPlugin(std::string const &name) const;
 
+        /**
+         * \brief Returns a pointer to plugin with given name
+         * 
+         * The behaviour is identical to GetPlugin, but it does not throw an exeption if the plugin
+         * is not found. Instead a null pointer is returned.
+         */
+        Plugin const *GetPluginQuiet(std::string const &name) const noexcept;
+
         /**
          * \brief Returns a pointer to plugin with given name. In addition checks that the plugin
          * is placed in the path before a plugin with name dependentName.
@@ -107,6 +115,16 @@ class Processor
          */
         Plugin const *GetPluginBefore(std::string const &name, std::string const &dependentName)
          const;
+
+        /**
+         * \brief Returns a pointer to plugin with given name. In addition checks that the plugin
+         * is placed in the path before a plugin with name dependentName.
+         * 
+         * Behaviour is identical to GetPluginBefore, but it does not throw an exception if the
+         * requested plugin is not found. Instead the method returns a null pointer.
+         */
+        Plugin const *GetPluginBeforeQuiet(std::string const &name,
+         std::string const &dependentName) const noexcept;
 
     private:
         /// Retuns index in the path of a plugin with given name. Throws an exception if not found

core/src/Processor.cpp

@@ -140,6 +140,19 @@ Plugin const *Processor::GetPlugin(string const &name) const
 }
 
 
+Plugin const *Processor::GetPluginQuiet(string const &name) const noexcept
+{
+    try
+    {
+        return GetPlugin(name);
+    }
+    catch (...)
+    {
+        return nullptr;
+    }
+}
+
+
 Plugin const *Processor::GetPluginBefore(string const &name, string const &dependentName) const
 {
     unsigned const indexInterest = GetPluginIndex(name);
@@ -153,6 +166,20 @@ Plugin const *Processor::GetPluginBefore(string const &name, string const &depen
 }
 
 
+Plugin const *Processor::GetPluginBeforeQuiet(string const &name, string const &dependentName) const
+ noexcept
+{
+    try
+    {
+        return GetPluginBefore(name, dependentName);
+    }
+    catch (...)
+    {
+        return nullptr;
+    }
+}
+
+
 unsigned Processor::GetPluginIndex(string const &name) const
 {
     unsigned index;