Debugger: Fix #12291.

UiUtils:
- Fix incorrect check to see if we had hit the bounds of the current memory
  block that would cause us to overflow the block's data buffer if incorrect
  length values were passed in.

src/apps/debugger/user_interface/util/UiUtils.cpp

@@ -337,6 +337,9 @@ UiUtils::DumpMemory(BString& _output, int32 indentLevel,
 	int32 j;
 	_output.Append('\t', indentLevel);
 	for (int32 i = 0; i < count; i++) {
+		if (!block->Contains(address + i * itemSize))
+			break;
+
 		uint8* value;
 
 		if ((i % displayWidth) == 0) {
@@ -350,8 +353,6 @@ UiUtils::DumpMemory(BString& _output, int32 indentLevel,
 			_output += data;
 			char c;
 			for (j = 0; j < displayed; j++) {
-				if (!block->Contains(address + displayed))
-					break;
 				c = *(block->Data() + address - block->BaseAddress()
 					+ (i * itemSize) + j);
 				if (!isprint(c))