Path for placeholder image was one to many folders up.

CURA-9146

plugins/Marketplace/resources/qml/CompatibilityDialog.qml

@@ -67,7 +67,7 @@ UM.Dialog
                             Image
                             {
                                 id: packageIcon
-                                source: model.icon_url || Qt.resolvedUrl("../../images/placeholder.svg")
+                                source: model.icon_url || Qt.resolvedUrl("../images/placeholder.svg")
                                 height: lineHeight
                                 width: height
                                 sourceSize.height: height
@@ -109,7 +109,7 @@ UM.Dialog
                             Image
                             {
                                 id: packageIcon
-                                source: model.icon_url || Qt.resolvedUrl("../../images/placeholder.svg")
+                                source: model.icon_url || Qt.resolvedUrl("../images/placeholder.svg")
                                 height: lineHeight
                                 width: height
                                 sourceSize.height: height

plugins/Marketplace/resources/qml/MultipleLicenseDialog.qml

@@ -51,7 +51,7 @@ UM.Dialog
                 sourceSize.width: width
                 sourceSize.height: height
                 fillMode: Image.PreserveAspectFit
-                source: licenseModel.iconUrl || Qt.resolvedUrl("../../images/placeholder.svg")
+                source: licenseModel.iconUrl || Qt.resolvedUrl("../images/placeholder.svg")
                 mipmap: true
             }