Fixed bug where method calls containing struct arguments would fail silently

Summary:
The arg block for handling structs did not return a value, which was being intepreted as failure. This diff returns YES for success, and also adds an error log for this case so future regressions won't fail silently.

Examples/UIExplorer/UIExplorerUnitTests/RCTModuleMethodTests.m

@@ -35,6 +35,9 @@ static BOOL RCTLogsError(void (^block)(void))
 @end
 
 @implementation RCTModuleMethodTests
+{
+  CGRect _s;
+}
 
 - (void)doFooWithBar:(__unused NSString *)bar { }
 
@@ -56,6 +59,7 @@ static BOOL RCTLogsError(void (^block)(void))
 - (void)doFooWithNumber:(__unused NSNumber *)n { }
 - (void)doFooWithDouble:(__unused double)n { }
 - (void)doFooWithInteger:(__unused NSInteger)n { }
+- (void)doFooWithCGRect:(CGRect)s { _s = s; }
 
 - (void)testNumbersNonnull
 {
@@ -102,4 +106,16 @@ static BOOL RCTLogsError(void (^block)(void))
   }
 }
 
+- (void)testStructArgument
+{
+  NSString *methodName = @"doFooWithCGRect:(CGRect)s";
+  RCTModuleMethod *method = [[RCTModuleMethod alloc] initWithObjCMethodName:methodName
+                                                               JSMethodName:nil
+                                                                moduleClass:[self class]];
+
+  CGRect r = CGRectMake(10, 20, 30, 40);
+  [method invokeWithBridge:nil module:self arguments:@[@[@10, @20, @30, @40]]];
+  XCTAssertTrue(CGRectEqualToRect(r, _s));
+}
+
 @end