Prevent "installation" of nonexistent builds

It's possible to click "Install" when there are no builds to choose
from, resulting in a (seemingly common) error[0]. There are a few
interlinked issues at play here. One is that we don't have strict
null checks on, that Underscore's type signatures don't acknowledge
`undefined` as a possible return value, and that a game is
considered installable if there are no errors, and we're not
calling the API. What it doesn't consider is the possibility that
the API tells us that there's nothing available.

I've resolved this at the earliest point in the user experience, by
redefining "installability" to include the presence of an
installable build. The other issues regarding nullability are still
present, but aren't practically a concern from what I've been able
to reproduce.

[0]https://itch.io/t/1112356/cannot-read-property-build-of-undefined-error-when-trying-to-install-games

src/renderer/modal-widgets/PlanInstall/index.tsx

@@ -181,7 +181,7 @@ class PlanInstall extends React.PureComponent<Props, State> {
       error,
     } = this.state;
 
-    let canInstall = !error && !busy;
+    let canInstall = !error && !busy && uploads && uploads.length > 0;
     let locationOptions = installLocations.map((il) => {
       let val: InstallLocationOption = {
         label: `${il.path} (${fileSize(il.sizeInfo.freeSize)} free)`,
@@ -251,6 +251,8 @@ class PlanInstall extends React.PureComponent<Props, State> {
           ? this.renderBusy()
           : error
           ? this.renderError()
+          : uploads && uploads.length == 0
+          ? this.renderNoBuilds()
           : this.renderSizes()}
         <Filler />
         <ModalButtons>
@@ -317,6 +319,16 @@ class PlanInstall extends React.PureComponent<Props, State> {
     );
   }
 
+  renderNoBuilds() {
+    return (
+      <ErrorContainer>
+        <ErrorParagraph>
+          <Icon icon="error" /> {T(_("plan_install.no_available_downloads"))}
+        </ErrorParagraph>
+      </ErrorContainer>
+    );
+  }
+
   renderSizes() {
     const { info, pickedInstallLocationId, installLocations } = this.state;
     if (!info) {

src/static/locales/en.json

@@ -700,5 +700,7 @@
   "plan_install.disk_space_required": "Disk space required",
   "plan_install.disk_space_available": "Disk space available",
 
+  "plan_install.no_available_downloads": "No compatible downloads were found",
+
   "empty_state.nothing_to_see_here": "Nothing to see here"
 }