Fix incorrect shader selection for text labels with inline images (#4082)

metrics/integration/render-tests/text-field/formatted-images-mixed/style.json

@@ -0,0 +1,59 @@
+{
+  "version": 8,
+  "metadata": {
+    "test": {
+      "height": 128,
+      "width": 128
+    }
+  },
+  "center": [ 0, 0 ],
+  "zoom": 0,
+  "sources": {
+    "point": {
+      "type": "geojson",
+      "data": {
+        "type": "FeatureCollection",
+        "features": [
+          {
+            "type": "Feature",
+            "geometry": {
+              "type": "Point",
+              "coordinates": [ 0, 20 ]
+            },
+            "properties": {
+              "iconsInText": "yes"
+            }
+          },
+          {
+            "type": "Feature",
+            "geometry": {
+              "type": "Point",
+              "coordinates": [ 0, -20 ]
+            }
+          }
+        ]
+      }
+    }
+  },
+  "glyphs": "local://glyphs/{fontstack}/{range}.pbf",
+  "sprite": "local://sprites/emerald@2x",
+  "layers": [
+    {
+      "id": "text",
+      "type": "symbol",
+      "source": "point",
+      "layout": {
+        "text-field": [
+          "case",
+          ["==", ["get", "iconsInText"], "yes"],
+          ["format", "IconsInText", ["image", "london-underground"]],
+          ["format", "TextOnly"]
+        ],
+        "text-font": [
+          "Open Sans Semibold",
+          "Arial Unicode MS Bold"
+        ]
+      }
+    }
+  ]
+}