make log-spacing explicit option for custom fit x values (#227)

closes #225

src/gui_qt/main/mainwindow.py

@@ -984,7 +984,8 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
         res = w.exec()
         if res:
             p = w.values
-            x = linspace(p[0], p[1], num=p[2])
+            spacefunc = geomspace if p[3] else linspace
+            x = spacefunc(p[0], p[1], num=p[2])
             self.management.extend_fits(sets, x)
 
     @QtCore.pyqtSlot(name='on_action_create_fit_function_triggered')

src/gui_qt/main/management.py

@@ -613,7 +613,7 @@ class UpperManagement(QtCore.QObject):
                 continue
 
             if not all(e is None for e in extrapolate):
-                spacefunc = np.geomspace if fit.islog else np.linspace
+                spacefunc = np.geomspace if extrapolate[3] else np.linspace
 
                 xmin = fit.x.min()
                 xmax = fit.x.max()