patcher: show errors on invalid json response from remote (#281)

## Link to GitHub Issue, if one exists
#0

## Description of change
When patcher URL returns an invalid response (as in, cannot be parsed as
JSON), show an error message to user.

Add a "copy text" button to copy the error message.

Fix WarnTooltip so that can handle the case where description is an
empty string for a patch - previously this was just showing as multiple
lines of empty space and then the warning.

## Compiling
It's fine except Docker build currently fails due to cmake version
issue.

## Testing
Tested valid / invalid datecodes and checked against responses.

src/spice2x/overlay/imgui/extensions.cpp

@@ -39,12 +39,12 @@ namespace ImGui {
 
         ImGui::BeginTooltip();
         ImGui::PushTextWrapPos(ImGui::GetFontSize() * 35.0f);
-        if (desc) {
+        if (desc && desc[0]) {
             ImGui::TextUnformatted(desc);
             ImGui::TextUnformatted("");
         }
         ImGui::PushStyleColor(ImGuiCol_Text, ImVec4(1.f, 1.f, 0.f, 1.f));
-        if (warn) {
+        if (warn && warn[0]) {
             ImGui::TextUnformatted("WARNING:");
             ImGui::TextUnformatted(warn);
         }