[Qt5 C++] Replace illegal characters in param names for Qt5 generator (#3978)

* Fix illegal characters in param names

* Re-generate the petstore sample

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/Qt5CPPGenerator.java

@@ -336,6 +336,33 @@ public class Qt5CPPGenerator extends DefaultCodegen implements CodegenConfig {
         }
     }
 
+    @Override
+    public String toVarName(String name) {
+        // sanitize name
+        name = sanitizeName(name); // FIXME: a parameter should not be assigned. Also declare the methods parameters as 'final'.
+
+        // if it's all uppper case, convert to lower case
+        if (name.matches("^[A-Z_]*$")) {
+            name = name.toLowerCase();
+        }
+
+        // camelize (lower first character) the variable name
+        // petId => pet_id
+        name = underscore(name);
+
+        // for reserved word or word starting with number, append _
+        if (isReservedWord(name) || name.matches("^\\d.*")) {
+            name = escapeReservedWord(name);
+        }
+
+        return name;
+    }
+
+    @Override
+    public String toParamName(String name) {
+        return toVarName(name);
+    }
+
     @Override
     public String toApiName(String type) {
         return PREFIX + Character.toUpperCase(type.charAt(0)) + type.substring(1) + "Api";