target: remove more exit() calls

These were all basically "can't happen" cases ... like having
state be corrupted by an alpha particle after the previous check
for whether a value was in-range.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/arm7_9_common.c

@@ -2362,10 +2362,6 @@ int arm7_9_read_memory(struct target *target, uint32_t address, uint32_t size, u
 				}
 			}
 			break;
-		default:
-			LOG_ERROR("BUG: we shouldn't get here");
-			exit(-1);
-			break;
 	}
 
 	if (!is_arm_mode(armv4_5->core_mode))
@@ -2546,10 +2542,6 @@ int arm7_9_write_memory(struct target *target, uint32_t address, uint32_t size,
 				num_accesses += thisrun_accesses;
 			}
 			break;
-		default:
-			LOG_ERROR("BUG: we shouldn't get here");
-			exit(-1);
-			break;
 	}
 
 	/* Re-Set DBGACK */

src/target/target.c

@@ -2154,8 +2154,9 @@ static void handle_md_output(struct command_context *cmd_ctx,
 	case 2: value_fmt = "%4.2x "; break;
 	case 1: value_fmt = "%2.2x "; break;
 	default:
+		/* "can't happen", caller checked */
 		LOG_ERROR("invalid memory read size: %u", size);
-		exit(-1);
+		return;
 	}
 
 	for (unsigned i = 0; i < count; i++)