label: max-width-chars should be ignored sometimes

When a widget is neither wrappable nor ellipsizable, we cannot modify
the label to fit into any size. So we cannot respect max-width-chars.

gtk/gtklabel.c

@@ -1082,7 +1082,7 @@ get_static_size (GtkLabel       *self,
 
   get_default_widths (self, &minimum_default, &natural_default);
 
-  layout = gtk_label_get_measuring_layout (self, NULL, natural_default);
+  layout = gtk_label_get_measuring_layout (self, NULL, self->ellipsize ? natural_default : -1);
 
   if (orientation == GTK_ORIENTATION_HORIZONTAL)
     {

testsuite/reftests/label-small-max-width-chars.ref.ui

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <object class="GtkWindow" id="window1">
+    <property name="decorated">0</property>
+    <child>
+      <object class="GtkLabel" id="label1">
+        <property name="label">Hello World</property>
+      </object>
+    </child>
+  </object>
+</interface>

testsuite/reftests/label-small-max-width-chars.ui

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <object class="GtkWindow" id="window1">
+    <property name="decorated">0</property>
+    <child>
+      <object class="GtkLabel" id="label1">
+        <property name="label">Hello World</property>
+        <property name="max-width-chars">2</property>
+      </object>
+    </child>
+  </object>
+</interface>

testsuite/reftests/meson.build

@@ -359,6 +359,8 @@ testdata = [
   'label-sizing.ui',
   'label-small-ellipsized.ref.ui',
   'label-small-ellipsized.ui',
+  'label-small-max-width-chars.ref.ui',
+  'label-small-max-width-chars.ui',
   'label-text-shadow-clipping.css',
   'label-text-shadow-clipping.ref.ui',
   'label-text-shadow-clipping.ui',