fix: add nullptr check when retrieving text run on iOS at the artboard

Issue: https://github.com/rive-app/rive-ios/issues/286

Doing a small check on the artboard query for a text run for `nullptr` before returning from the Artboard

Diffs=
35daf194f fix: add nullptr check when retrieving text run on iOS at the artboard (#6312)

Co-authored-by: Zachary Plata <plata.zach@gmail.com>

.rive_head

@@ -1 +1 @@
-fabb7f97fe7b69368c9a7369febfecbc90be49cd
+35daf194f427d04fb4a906f8162a1da53709aa5d

.rive_renderer

@@ -1 +1 @@
-7b7595392d849217e43a829b71dfad58ecf29b06
+683bae68fa2a0cf8515f2dbfb35bdd0c3a298ecd

Example-iOS/Source/Examples/SwiftUI/SwiftTestText.swift

@@ -24,7 +24,11 @@ struct TextInputView: DismissableView {
                 .padding()
                 .onChange(of: userInput, perform: { newValue in
                     if (!newValue.isEmpty) {
-                        try! rvm.setTextRunValue("MyRun", textValue: userInput)
+                        do {
+                           try rvm.setTextRunValue("MyRun", textValue: userInput)
+                        } catch {
+                            debugPrint(error)
+                        }
                     }
                 })
             rvm.view()

Source/Renderer/RiveArtboard.mm

@@ -221,7 +221,11 @@ static int artInstanceCount = 0;
 {
     const std::string stdName = std::string([name UTF8String]);
     auto riveTextRun = _artboardInstance->find<rive::TextValueRun>(stdName);
-    return [[RiveTextValueRun alloc] initWithTextValueRun:std::move(riveTextRun)];
+    if (riveTextRun != nullptr)
+    {
+        return [[RiveTextValueRun alloc] initWithTextValueRun:std::move(riveTextRun)];
+    }
+    return nullptr;
 }
 
 @end

Tests/RiveArtboardLoadTest.mm

@@ -141,4 +141,13 @@
     XCTAssertTrue([[textRun text] isEqualToString:@"Hello text"]);
 }
 
+- (void)testCatchingErrorOnBadTextRun
+{
+    RiveFile* file = [Util loadTestFile:@"testtext" error:nil];
+    NSError* error = nil;
+    RiveArtboard* artboard = [file artboardFromName:@"New Artboard" error:&error];
+    RiveTextValueRun* textRun = [artboard textRun:@"BADRUN"];
+    XCTAssertNil(textRun);
+}
+
 @end