Fixes return type of Fl_Input_::dvalue()

FL/Fl_Input_.H

@@ -264,7 +264,7 @@ public:
 
   int ivalue() const;
 
-  int dvalue() const;
+  double dvalue() const;
 
   /* Returns the Unicode character at index \p i. */
   unsigned int index(int i) const;

src/Fl_Input_.cxx

@@ -1506,7 +1506,7 @@ int Fl_Input_::ivalue() const {
  \see Fl_Input_::ivalue()
  \see Fl_Input_::value(double)
  */
-int Fl_Input_::dvalue() const {
+double Fl_Input_::dvalue() const {
   return atof(value());
 }