TextBox: preferred_size_impl() was unreliable

The following was detected by the new ``preferred_size()`` cache
consistency checks in debug mode.

``TextBox::preferred_size_impl()`` forgot to set the font and font size.
This meant the computed result was dependent on UI/sizing computation
done by other widgets previously :-(.

Author: wjakob

src/textbox.cpp

@@ -61,7 +61,10 @@ void TextBox::set_theme(Theme *theme) {
 }
 
 Vector2i TextBox::preferred_size_impl(NVGcontext *ctx) const {
-    Vector2i size(0, font_size() * 1.4f);
+    Vector2i size(0, m_font_size * 1.4f);
+
+    nvgFontFace(ctx, "sans");
+    nvgFontSize(ctx, m_font_size);
 
     float uw = 0;
     if (m_units_image > 0) {
@@ -79,6 +82,7 @@ Vector2i TextBox::preferred_size_impl(NVGcontext *ctx) const {
 
     float ts = nvgTextBounds(ctx, 0, 0, m_value.c_str(), nullptr, nullptr);
     size[0] = size[1] + ts + uw + sw;
+
     return size;
 }
 
@@ -125,7 +129,7 @@ void TextBox::draw(NVGcontext* ctx) {
     nvgStrokeColor(ctx, Color(0, 48));
     nvgStroke(ctx);
 
-    nvgFontSize(ctx, font_size());
+    nvgFontSize(ctx, m_font_size);
     nvgFontFace(ctx, "sans");
     Vector2i draw_pos(m_pos.x(), m_pos.y() + m_size.y() * 0.5f + 1);
 
@@ -187,7 +191,7 @@ void TextBox::draw(NVGcontext* ctx) {
             nvgText(ctx, icon_pos.x(), icon_pos.y(), icon.data(), nullptr);
         }
 
-        nvgFontSize(ctx, font_size());
+        nvgFontSize(ctx, m_font_size);
         nvgFontFace(ctx, "sans");
     }
 
@@ -206,7 +210,7 @@ void TextBox::draw(NVGcontext* ctx) {
             break;
     }
 
-    nvgFontSize(ctx, font_size());
+    nvgFontSize(ctx, m_font_size);
     nvgFillColor(ctx, m_enabled && (!m_committed || !m_value.empty()) ?
         m_theme->m_text_color :
         m_theme->m_disabled_text_color);