Fix a crash when copying with styles.

Add +[NSObject castFrom:]

sources/NSObject+iTerm.h

@@ -19,6 +19,7 @@
 @interface NSObject (iTerm)
 + (BOOL)object:(NSObject *)a isEqualToObject:(NSObject *)b;
++ (instancetype)castFrom:(id)object;
 - (void)performSelectorOnMainThread:(SEL)selector withObjects:(NSArray *)objects;

sources/NSObject+iTerm.m

@@ -20,6 +20,14 @@
     return [a isEqual:b];
 }
++ (instancetype)castFrom:(id)object {
+    if ([object isKindOfClass:[self class]]) {
+        return object;
+    } else {
+        return self;
+    }
+}
+
 - (void)performSelectorWithObjects:(NSArray *)tuple {
     SEL selector = NSSelectorFromString(tuple[0]);
     NSArray *objects = tuple[1];

sources/PTYTextView.m

@@ -44,6 +44,7 @@
 #import "NSFileManager+iTerm.h"
 #import "NSImage+iTerm.h"
 #import "NSMutableAttributedString+iTerm.h"
+#import "NSObject+iTerm.h"
 #import "NSPasteboard+iTerm.h"
 #import "NSStringITerm.h"
 #import "NSURL+iTerm.h"
@@ -3239,7 +3240,8 @@ static double EuclideanDistance(NSPoint p1, NSPoint p2) {
             } else {
                 [theSelectedText appendString:content];
             }
-            if (eol && ![content hasSuffix:@"\n"]) {
+            NSString *contentString = attributed ? [content string] : content;
+            if (eol && ![contentString hasSuffix:@"\n"]) {
                 if (attributed) {
                     [theSelectedText iterm_appendString:@"\n"];
                 } else {