Mute some warnings (#6563)

rtgui/main-cli.cc

@@ -290,6 +290,7 @@ int processLineParams ( int argc, char **argv )
 
                 case 'O':
                     copyParamsFile = true;
+                    // fall through
 
                 case 'o': // outputfile or dir
                     if ( iArg + 1 < argc ) {
@@ -341,6 +342,7 @@ int processLineParams ( int argc, char **argv )
 
                 case 'S':
                     skipIfNoSidecar = true;
+                    // fall through
 
                 case 's': // Processing params next to file (file extension appended)
                     sideProcParams = true;

rtgui/main.cc

@@ -169,7 +169,7 @@ int processLineParams ( int argc, char **argv )
                         break;
                     }
 
-                // no break here on purpose
+                // fall through
 
                 case 'h':
                 case '?':

rtgui/rtimage.cc

@@ -38,7 +38,7 @@ int RTImage::scaleBack = 0;
 
 RTImage::RTImage () {}
 
-RTImage::RTImage (RTImage &other) : surface(other.surface), pixbuf(other.pixbuf)
+RTImage::RTImage (RTImage &other) : Gtk::Image(), surface(other.surface), pixbuf(other.pixbuf)
 {
     if (pixbuf) {
         set(pixbuf);