+ do not allow negative numbers in fillet and chamfer panel

src/Mod/PartDesign/Gui/TaskChamferParameters.cpp

@@ -67,6 +67,7 @@ TaskChamferParameters::TaskChamferParameters(ViewProviderChamfer *ChamferView,QW
 
     ui->chamferDistance->setUnit(Base::Unit::Length);
     ui->chamferDistance->setValue(r);
+    ui->chamferDistance->setMinimum(0);
     ui->chamferDistance->selectNumber();
     QMetaObject::invokeMethod(ui->chamferDistance, "setFocus", Qt::QueuedConnection);
 }

src/Mod/PartDesign/Gui/TaskFilletParameters.cpp

@@ -67,6 +67,7 @@ TaskFilletParameters::TaskFilletParameters(ViewProviderFillet *FilletView,QWidge
 
     ui->filletRadius->setUnit(Base::Unit::Length);
     ui->filletRadius->setValue(r);
+    ui->filletRadius->setMinimum(0);
     ui->filletRadius->selectNumber();
     QMetaObject::invokeMethod(ui->filletRadius, "setFocus", Qt::QueuedConnection);
 }